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Texas water development board  the manual texas on rainwater harverting Texas water development board the manual texas on rainwater harverting Document Transcript

  • The Texas Manual onRainwater Harvesting Texas Water Development Board Third Edition
  • The Texas Manual on Rainwater Harvesting Texas Water Development Board in cooperation with Chris Brown Consulting Jan Gerston Consulting Stephen Colley/Architecture Dr. Hari J. Krishna, P.E., Contract Manager Third Edition 2005 Austin, Texas
  • AcknowledgmentsThe authors would like to thank the following persons for their assistance with theproduction of this guide: Dr. Hari Krishna, Contract Manager, Texas Water DevelopmentBoard, and President, American Rainwater Catchment Systems Association (ARCSA);Jen and Paul Radlet, Save the Rain; Richard Heinichen, Tank Town; John Kight, KendallCounty Commissioner and Save the Rain board member; Katherine Crawford, GoldenEagle Landscapes; Carolyn Hall, Timbertanks; Dr. Howard Blatt, Feather & Fur AnimalHospital; Dan Wilcox, Advanced Micro Devices; Ron Kreykes, ARCSA board member;Dan Pomerening and Mary Dunford, Bexar County; Billy Kniffen, Menard CountyCooperative Extension; Javier Hernandez, Edwards Aquifer Authority; Lara Stuart, CBC;Wendi Kimura, CBC. We also acknowledge the authors of the previous edition of thispublication, The Texas Guide to Rainwater Harvesting, Gail Vittori and Wendy PriceTodd, AIA. DisclaimerThe use of brand names in this publication does not indicate an endorsement by the TexasWater Development Board, or the State of Texas, or any other entity.Views expressed in this report are of the authors and do not necessarily reflect the viewsof the Texas Water Development Board, or any other entity.
  • Table of ContentsChapter 1 Introduction..................................................................................................... 1Chapter 2 Rainwater Harvesting System Components................................................. 5 Basic Components .......................................................................................................... 5 The Catchment Surface................................................................................................... 5 Gutters and Downspouts ................................................................................................. 6 Leaf Screens.................................................................................................................... 7 First-Flush Diverters ....................................................................................................... 8 Roof Washers................................................................................................................ 10 Storage Tanks................................................................................................................ 10 Pressure Tanks and Pumps............................................................................................ 16 Treatment and Disinfection Equipment ........................................................................ 17Chapter 3 Water Quality and Treatment..................................................................... 21 Considerations for the Rainwater Harvesting System Owner ...................................... 21 Water Quality Standards ............................................................................................... 22 Factors Affecting Water Quality................................................................................... 22 Water Treatment ........................................................................................................... 23Chapter 4 Water Balance and System Sizing............................................................... 29 How Much Water Can Be Captured? ........................................................................... 29 Rainfall Distribution ..................................................................................................... 30 Calculating Storage Capacity........................................................................................ 32 The Water Balance Method Using Monthly Demand and Supply ............................... 32 Estimating Demand....................................................................................................... 33 Estimating indoor water demand .............................................................................. 33 Indoor water conservation......................................................................................... 35 Estimating outdoor water demand ............................................................................ 36Chapter 5 Rainwater Harvesting Guidelines ............................................................... 41 RWH Best Management Practices................................................................................ 41 Water Conservation Implementation Task Force Guidelines................................... 41 American Rainwater Catchment Systems Association............................................. 41 Building Codes.............................................................................................................. 41 Cistern Design, Construction, and Capacity ................................................................. 42 Backflow Prevention and Dual-Use Systems ............................................................... 42 Required Rainwater Harvesting Systems...................................................................... 43Chapter 6 Cost Estimation............................................................................................. 45 Comparing to Other Sources of Water.......................................................................... 51 i
  • Chapter 7 Financial and Other Incentives ................................................................... 53 Tax Exemptions ............................................................................................................ 53 Municipal Incentives..................................................................................................... 54 Rainwater Harvesting at State Facilities ....................................................................... 55 Performance Contracting .............................................................................................. 56Appendix A References ................................................................................................. A1Appendix B Rainfall Data ............................................................................................. A7Appendix C Case Studies ............................................................................................ A11Appendix D Tax Exemption Application Form ........................................................ A25 ii
  • Chapter 1 IntroductionRainwater harvesting is an ancient extending their use; rainwatertechnique enjoying a revival in eliminates the need for a waterpopularity due to the inherent quality of softener and the salts added duringrainwater and interest in reducing the softening process.consumption of treated water. Rainwater is sodium-free, importantRainwater is valued for its purity and for persons on low-sodium diets.softness. It has a nearly neutral pH, and Rainwater is superior for landscapeis free from disinfection by-products, irrigation.salts, minerals, and other natural andman-made contaminants. Plants thrive Rainwater harvesting reduces flow tounder irrigation with stored rainwater. stormwater drains and also reducesAppliances last longer when free from non-point source pollution.the corrosive or scale effects of hard Rainwater harvesting helps utilitieswater. Users with potable systems prefer reduce the summer demand peak andthe superior taste and cleansing delay expansion of existing waterproperties of rainwater. treatment plants.Archeological evidence attests to the Rainwater harvesting reducescapture of rainwater as far back as 4,000 consumers’ utility bills.years ago, and the concept of rainwater Perhaps one of the most interestingharvesting in China may date back 6,000 aspects of rainwater harvesting isyears. Ruins of cisterns built as early as learning about the methods of capture,2000 B.C. for storing runoff from storage, and use of this natural resourcehillsides for agricultural and domestic at the place it occurs. This naturalpurposes are still standing in Israel synergy excludes at least a portion of(Gould and Nissen-Petersen, 1999). water use from the water distributionAdvantages and benefits of rainwater infrastructure: the centralized treatmentharvesting are numerous (Krishna, facility, storage structures, pumps,2003). mains, and laterals. The water is free; the only cost is for Rainwater harvesting also includes land- collection and use. based systems with man-made landscape The end use of harvested water is features to channel and concentrate located close to the source, rainwater in either storage basins or eliminating the need for complex and planted areas. costly distribution systems. When assessing the health risks of Rainwater provides a water source drinking rainwater, consider the path when groundwater is unacceptable or taken by the raindrop through a unavailable, or it can augment limited watershed into a reservoir, through groundwater supplies. public drinking water treatment and distribution systems to the end user. The zero hardness of rainwater helps Being the universal solvent, water prevent scale on appliances, absorbs contaminants and minerals on its 1
  • travels to the reservoir. While in of rainwater. The scope, method,residence in the reservoir, the water can technologies, system complexity,come in contact with all kinds of foreign purpose, and end uses vary from rainmaterials: oil, animal wastes, chemical barrels for garden irrigation in urbanand pharmaceutical wastes, organic areas, to large-scale collection ofcompounds, industrial outflows, and rainwater for all domestic uses. Sometrash. It is the job of the water treatment examples are summarized below:plant to remove harmful contaminants For supplemental irrigation water, theand to kill pathogens. Unfortunately, Wells Branch Municipal Utilitywhen chlorine is used for disinfection, it District in North Austin capturesalso degrades into disinfection by- rainwater, along with air conditioningproducts, notably trihalomethanes, condensate, from a new 10,000-which may pose health risks. In contrast, square-foot recreation center into athe raindrop harvested on site will travel 37,000-gallon tank to serve asdown a roof via a gutter to a storage irrigation water for a 12-acretank. Before it can be used for drinking, municipal park with soccer fields andit will be treated by a relatively simple offices.process with equipment that occupiesabout 9 cubic feet of space. The Lady Bird Johnson Wildflower Research Center in Austin, Texas,Rainwater harvesting can reduce the harvests 300,000 gallons of rainwatervolume of storm water, thereby annually from almost 19,000 squarelessening the impact on erosion and feet of roof collection area fordecreasing the load on storm sewers. irrigation of its native plantDecreasing storm water volume also landscapes. A 6,000-gallon stonehelps keep potential storm water cistern and its arching stone aqueductpollutants, such as pesticides, fertilizers, form the distinctive entry to theand petroleum products, out of rivers research center.and groundwater. The Advanced Micro DevicesBut along with the independence of semiconductor fabrication plant inrainwater harvesting systems comes the Austin, Texas, does not use utility-inherent responsibility of operation and supplied water for irrigation, savingmaintenance. For all systems, this $1.5 million per year by relying onresponsibility includes purging the first- captured rainwater and collectedflush system, regularly cleaning roof groundwater.washers and tanks, maintaining pumps,and filtering water. For potable systems, Reynolds Metals in Ingleside, Texas,responsibilities include all of the above, uses stormwater captured inand the owner must replace cartridge containment basins as process waterfilters and maintain disinfection in its metal-processing plant, greatlyequipment on schedule, arrange to have offsetting the volume of purchasedwater tested, and monitor tank levels. water.Rainwater used for drinking should be The city of Columbia, Nuevo León,tested, at a minimum, for pathogens. Mexico, is in the planning stages ofRainwater harvesting, in its essence, is developing rainwater as the basis forthe collection, conveyance, and storage the city’s water supply for new 2
  • growth areas, with large industrial In fact, rainwater harvesting is developments being plumbed for encouraged by Austin and San Antonio storage and catchment. water utilities as a means of conserving On small volcanic or coral islands, water. The State of Texas also offers rainwater harvesting is often the only financial incentives for rainwater option for public water supply, as harvesting systems. Senate Bill 2 of the watersheds are too small to create a 77th Legislature exempts rainwater major river, and groundwater is either harvesting equipment from sales tax, and nonexistent or contaminated with salt allows local governments to exempt water. Bermuda, the U.S. Virgin rainwater harvesting systems from ad Islands, and other Caribbean islands valorem (property) taxes. require cisterns to be included with all Rainwater harvesting systems can be as new construction. simple as a rain barrel for gardenIn Central Texas, more than 400 full- irrigation at the end of a downspout, orscale rainwater harvesting systems have as complex as a domestic potable systembeen installed by professional or a multiple end-use system at a largecompanies, and more than 6,000 rain corporate campus.barrels have been installed through the Rainwater harvesting is practical onlyCity of Austin’s incentive program in the when the volume and frequency ofpast decade. Countless “do-it- rainfall and size of the catchment surfaceyourselfers” have installed systems over can generate sufficient water for thethe same time period. intended purpose.An estimated 100,000 residential From a financial perspective, therainwater harvesting systems are in use installation and maintenance costs of ain the United States and its territories rainwater harvesting system for potable(Lye, 2002). More are being installed by water cannot compete with waterthe urban home gardener seeking supplied by a central utility, but is oftenhealthier plants, the weekend cabin cost-competitive with installation of aowner, and the homeowner intent upon well in rural settings.the “green” building practices – all With a very large catchment surface,seeking a sustainable, high-quality water such as that of big commercial building,source. Rainwater harvesting is also the volume of rainwater, when capturedrecognized as an important water- and stored, can cost-effectively serveconserving measure, and is best several end uses, such as landscapeimplemented in conjunction with other irrigation and toilet flushing.efficiency measures in and outside of thehome. Some commercial and industrial buildings augment rainwater withHarvested rainwater may also help some condensate from air conditioningTexas communities close the gap systems. During hot, humid months,between supply and demand projected warm, moisture-laden air passing overby the Texas Water Development Board the cooling coils of a residential air(TWDB), as the state’s population nearly conditioner can produce 10 or moredoubles between 2000 and 2050 (Texas gallons per day of water. IndustrialWater Development Board, 2002). facilities produce thousands of gallons 3
  • per day of condensate. An advantage of Referencescondensate capture is that its maximum Gould J, Nissen-Petersen E. 1999.production occurs during the hottest Rainwater catchment systems formonth of the year, when irrigation need domestic rain: design constructionis greatest. Most systems pipe and implementation. London:condensate into the rainwater cistern for Intermediate Technologystorage. Publications. 335 p.The depletion of groundwater sources, Krishna H. 2003. An overview ofthe poor quality of some groundwater, rainwater harvesting systems andhigh tap fees for isolated properties, the guidelines in the United States.flexibility of rainwater harvesting Proceedings of the First Americansystems, and modern methods of Rainwater Harvesting Conference;treatment provide excellent reasons to 2003 Aug 21-23; Austin (TX).harvest rainwater for domestic use. Lye D. 2002. Health risks associatedThe scope of this manual is to serve as a with consumption of untreated waterprimer in the basics of residential and from household roof catchmentsmall-scale commercial rainwater systems. Journal of the Americanharvesting systems design. It is intended Water Resources Associationto serve as a first step in thinking about 38(5):1301-1306.options for implementing rainwaterharvesting systems, as well as Texas Water Development Board. 2002.advantages and constraints. Water for Texas – 2002. Austin (TX): Texas Water Development Board. 155 p. 4
  • Chapter 2 Rainwater Harvesting System ComponentsRainwater harvesting is the capture, building code officer should bediversion, and storage of rainwater for a consulted concerning safe, sanitarynumber of different purposes including operations and construction of theselandscape irrigation, drinking and systems.domestic use, aquifer recharge, andstormwater abatement. Basic ComponentsIn a residential or small-scale Regardless of the complexity of theapplication, rainwater harvesting can be system, the domestic rainwateras simple as channeling rain running off harvesting system (Figure 2-1)an unguttered roof to a planted landscape comprises six basic components:area via contoured landscape. To prevent Catchment surface: the collectionerosion on sloped surfaces, a bermed surface from which rainfall runs offconcave holding area down slope can Gutters and downspouts: channelstore water for direct use by turfgrass or water from the roof to the tankplants (Waterfall, 1998). More complexsystems include gutters, pipes, storage Leaf screens, first-flush diverters, andtanks or cisterns, filtering, pump(s), and roof washers: components whichwater treatment for potable use. remove debris and dust from the captured rainwater before it goes toThis chapter focuses on residential or the tanksmall-scale commercial systems, forboth irrigation and potable use. One or more storage tanks, also called cisternsThe local health department and city Delivery system: gravity-fed or pumped to the end use Treatment/purification: for potable systems, filters and other methods to make the water safe to drink The Catchment Surface The roof of a building or house is the obvious first choice for catchment. For additional capacity, an open-sided barn – called a rain barn or pole barn – can be built. Water tanks and other rainwater system equipment, such as pumps and filters, as well as vehicles, bicycles, and gardening tools, can be stored under the barn. Water quality from different roof Figure 2-1. Typical rainwater harvesting catchments is a function of the type of installation roof material, climatic conditions, and 5
  • the surrounding environment harvested is usually suitable only for(Vasudevan, 2002). irrigation due to leaching of compounds.Metal Slate. Slate’s smoothness makes it idealThe quantity of rainwater that can be for a catchment surface for potable use,collected from a roof is in part a function assuming no toxic sealant is used;of the roof texture: the smoother the however, cost considerations maybetter. A commonly used roofing preclude its use.material for rainwater harvesting is soldunder the trade name Galvalume®, a 55 Gutters and Downspoutspercent aluminum/45 percent zinc alloy- Gutters are installed to capture rainwatercoated sheet steel. Galvalume® is also running off the eaves of a building.available with a baked enamel coating, Some gutter installers can provideor it can be painted with epoxy paint. continuous or seamless gutters.Some caution should be exercised For potable water systems, lead cannotregarding roof components. Roofs with be used as gutter solder, as is sometimescopper flashings can cause discoloration the case in older metal gutters. Theof porcelain fixtures. slightly acidic quality of rain could dissolve lead and thus contaminate theClay/concrete tile water supply.Clay and concrete tiles are both porous. The most common materials for guttersEasily available materials are suitable and downspouts are half-round PVC,for potable or nonpotable systems, but vinyl, pipe, seamless aluminum, andmay contribute to as much as a 10- galvanized steel.percent loss due to texture, inefficientflow, or evaporation. To reduce water Seamless aluminum gutters are usuallyloss, tiles can be painted or coated with a installed by professionals, and, therefore,sealant. There is some chance of toxins are more expensive than other options.leaching from the tile sealant or paint, Regardless of material, other necessarybut this roof surface is safer when components in addition to the horizontalpainted with a special sealant or paint to gutters are the drop outlet, which routesprevent bacterial growth on porous water from the gutters downward and atmaterials. least two 45-degree elbows which allowComposite or asphalt shingle the downspout pipe to snug to the side ofDue to leaching of toxins, composite the house. Additional componentsshingles are not appropriate for potable include the hardware, brackets, andsystems, but can be used to collect water straps to fasten the gutters andfor irrigation. Composite roofs have an downspout to the fascia and the wall.approximated 10-percent loss due to Gutter Sizing and Installationinefficient flow or evaporation (Radlet When using the roof of a house as aand Radlet, 2004). catchment surface, it is important toOthers consider that many roofs consist of oneWood shingle, tar, and gravel. These or more roof “valleys.” A roof valleyroofing materials are rare, and the water occurs where two roof planes meet. This is most common and easy to visualize 6
  • when considering a house plan with an both before and after the storage tank.“L” or “T” configuration. A roof valley The defense in keeping debris out of aconcentrates rainfall runoff from two rainwater harvesting system is some typeroof planes before the collected rain of leaf screen along the gutter or in thereaches a gutter. Depending on the size downspout.of roof areas terminating in a roof valley, Depending upon the amount and type ofthe slope of the roofs, and the intensity tree litter and dust accumulation, theof rainfall, the portion of gutter located homeowner may have to experiment towhere the valley water leaves the eave of find the method that works best. Leafthe roof may not be able to capture all screens must be regularly cleaned to bethe water at that point, resulting in effective. If not maintained, leaf screensspillage or overrunning. can become clogged and preventBesides the presence of one or more roof rainwater from flowing into a tank.valleys, other factors that may result in Built-up debris can also harbor bacteriaoverrunning of gutters include an and the products of leaf decay.inadequate number of downspouts, Leaf guards are usually ¼-inch meshexcessively long roof distances from screens in wire frames that fit along theridge to eave, steep roof slopes, and length of the gutter. Leaf guards/screensinadequate gutter maintenance. are usually necessary only in locationsVariables such as these make any gutter with tree overhang. Guards with profilessizing rules of thumb difficult to apply. conducive to allowing leaf litter to slideConsult you gutter supplier about your off are also available.situation with special attention todetermine where gutter overrunning The funnel-type downspout filter isareas may occur. At these points along made of PVC or galvanized steel fittedan eave, apply strategies to minimize with a stainless steel or brass screen.possible overrunning to improve This type of filter offers the advantage ofcatchment efficiency. Preventative easy accessibility for cleaning. Thestrategies may include modifications to funnel is cut into the downspout pipe atthe size and configuration of gutters and the same height or slightly higher thanaddition of gutter boxes with the highest water level in the storagedownspouts and roof diverters near the tank.eave edge. Strainer baskets are spherical cage-likeGutters should be installed with slope strainers that slip into the drop outlet oftowards the downspout; also the outside the downspout.face of the gutter should be lower than A cylinder of rolled screen inserted intothe inside face to encourage drainage the drop outlet serves as another methodaway from the building wall. of filtering debris. The homeowner may need to experiment with various gridLeaf Screens sizes, from insect screen to hardwareTo remove debris that gathers on the cloth.catchment surface, and ensure highquality water for either potable use or to Filter socks of nylon mesh can bework well without clogging irrigation installed on the PVC pipe at the tankemitters, a series of filters are necessary. inflow.Essentially, mesh screens remove debris 7
  • First-Flush Diverters A preliminary study by Rain WaterA roof can be a natural collection Harvesting and Waste Water Systemssurface for dust, leaves, blooms, twigs, Pty Ltd., a rainwater harvestinginsect bodies, animal feces, pesticides, component vendor in Australia,and other airborne residues. The first- recommends that between 13 and 49flush diverter routes the first flow of gallons be diverted per 1,000 square feet.water from the catchment surface away The primary reason for the widefrom the storage tank. The flushed water variation in estimates is that there is nocan be routed to a planted area. While exact calculation to determine how muchleaf screens remove the larger debris, initial water needs to be diverted becausesuch as leaves, twigs, and blooms that there are many variables that wouldfall on the roof, the first-flush diverter determine the effectiveness of washinggives the system a chance to rid itself of the contaminants off the collectionthe smaller contaminants, such as dust, surface, just as there are many variablespollen, and bird and rodent feces. determining the make up of theThe simplest first-flush diverter is a PVC contaminants themselves. For example,standpipe (Figure 2-2). The standpipe the slope and smoothness of thefills with water first during a rainfall collection surface, the intensity of theevent; the balance of water is routed to rain event, the length of time betweenthe tank. The standpipe is drained events (which adds to the amount ofcontinuously via a pinhole or by leaving accumulated contaminants), and thethe screw closure slightly loose. In any nature of the contaminants themselvescase, cleaning of the standpipe is add to the difficulty of determining justaccomplished by removing the PVC how much rain should be diverted duringcover with a wrench and removing first flush. In order to effectively wash acollected debris after each rainfall event. collection surface, a rain intensity of one-tenth of an inch of rain per hour isThere are several other types of first- needed to wash a sloped roof. A flat orflush diverters. The ball valve type near-flat collection surface requires 0.18consists of a floating ball that seals off inches of rain per hour for an effectivethe top of the diverter pipe (Figure 2-3) washing of the surface.when the pipe files with water. The recommended diversion of firstOpinions vary on the volume of flush ranges from one to two gallons ofrainwater to divert. The number of dry first-flush diversion for each 100 squaredays, amount of debris, and roof surface feet of collection area. If using a roof forare all variables to consider. a collection area that drains into gutters,One rule of thumb for first-flush calculate the amount of rainfall area thatdiversion is to divert a minimum of 10 will be drained into every gutter feedinggallons for every 1,000 square feet of your system. Remember to calculate thecollection surface. However, first-flush horizontal equivalent of the “roofvolumes vary with the amount of dust on footprint” when calculating yourthe roof surface, which is a function of catchment area. (Please refer to thethe number of dry days, the amount and Figure 4-1 in Chapter 4, Water Balancetype of debris, tree overhang, and and System Sizing.) If a gutter receivesseason. the quantity of runoff that require multiple downspouts, first-flush 8
  • First-Flush Diverters Standpipe The simplest first-flush diverter is a 6- or 8-inch PVC standpipe (Figure 2-2). The diverter fills with water first, backs up, and then allows water to flow into the main collection piping. These standpipes usually have a cleanout fitting at the bottom, and must be emptied and cleaned out after each rainfall event. The water from the standpipe may be routed to a planted area. A pinhole drilled at the bottom of the pipe or a hose bibb fixture left slightly open (shown) allows water to gradually leak out. If you are using 3” diameter PVC or similar pipe, allow 33” length of pipe per gallon; 4” diameter pipe needs only 18” of length per gallon; and a little over 8” of 6” diameter pipe is needed to catch a gallon of water. Figure 2-2. Standpipe first-flush diverterStandpipe with ball valveThe standpipe with ball valve is a variation ofthe standpipe filter. The cutaway drawing(Figure 2-3) shows the ball valve. As thechamber fills, the ball floats up and seals on theseat, trapping first-flush water and routing thebalance of the water to the tank. Figure 2-3. Standpipe with ball valve 9
  • diversion devices will be required for (handling rainwater from 1,500- andeach downspout. 3,500-square-foot catchments, respectively). The box is placed atop aRoof Washers ladder-like stand beside the tank, fromThe roof washer, placed just ahead of the which the system owner accesses thestorage tank, filters small debris for box for cleaning via the ladder. Inpotable systems and also for systems locations with limited drop, a filter withusing drip irrigation. Roof washers the canisters oriented horizontally isconsist of a tank, usually between 30- indicated, with the inlet and outlet of theand 50-gallon capacity, with leaf filter being nearly parallel.strainers and a filter (Figure 2-4). Onecommercially available roof washer has Storage Tanksa 30-micron filter. (A micron, also called The storage tank is the most expensivea micrometer, is one-millionth of a component of the rainwater harvestingmeter. A 30-micron filter has pores system.about one-third the diameter of a human The size of storage tank or cistern ishair.) dictated by several variables: theAll roof washers must be cleaned. rainwater supply (local precipitation),Without proper maintenance they not the demand, the projected length of dryonly become clogged and restrict the spells without rain, the catchmentflow of rainwater, but may themselves surface area, aesthetics, personalbecome breeding grounds for pathogens. preference, and budget.The box roof washer (Figure 2-4) is a A myriad of variations on storage tankscommercially available component and cisterns have been used over theconsisting of a fiberglass box with one centuries and in different geographicalor two 30-micron canister filters regions: earthenware cisterns in pre- biblical times, large pottery containers in Africa, above-ground vinyl-lined swimming pools in Hawaii, concrete or brick cisterns in the central United States, and, common to old homesteads in Texas, galvanized steel tanks and attractive site-built stone-and-mortar cisterns. For purposes of practicality, this manual will focus on the most common, easily installed, and readily available storage options in Texas, some still functional after a century of use. Storage tank basics Storage tanks must be opaque, either upon purchase or painted later, toFigure 2-4. Box roof washer inhibit algae growth. 10
  • For potable systems, storage tanks truck, preferably near a driveway or must never have been used to store roadway. toxic materials. Water weighs just over 8 pounds per Tanks must be covered and vents gallon, so even a relatively small 1,500- screened to discourage mosquito gallon tank will weigh 12,400 pounds. A breeding. leaning tank may collapse; therefore, Tanks used for potable systems must tanks should be placed on a stable, level be accessible for cleaning. pad. If the bed consists of a stable substrate, such as caliche, a load of sandStorage tank siting or pea gravel covering the bed may beTanks should be located as close to sufficient preparation. In some areas,supply and demand points as possible to sand or pea gravel over well-compactedreduce the distance water is conveyed. soil may be sufficient for a small tank.Storage tanks should be protected from Otherwise, a concrete pad should bedirect sunlight, if possible. To ease the constructed. When the condition of theload on the pump, tanks should be soil is unknown, enlisting the services ofplaced as high as practicable. Of course, a structural engineer may be in order tothe tank inlet must be lower than the ensure the stability of the soil supportinglowest downspout from the catchment the full cistern weight.area. To compensate for friction lossesin the trunk line, a difference of a couple Another consideration is protecting theof feet is preferable. When converting pad from being undermined by eitherfrom well water, or if using a well normal erosion or from the tankbackup, siting the tanks near the well overflow. The tank should be positionedhouse facilitates the use of existing such that runoff from other parts of theplumbing. property or from the tank overflow will not undermine the pad. The pad or bedWater runoff should not enter septic should be checked after intense rainfallsystem drainfields, and any tank events.overflow and drainage should be routedso that it does not affect the foundation Fiberglassof the tanks or any other structures Fiberglass tanks (Figure 2-5) are built in(Macomber, 2001). standard capacities from 50 gallons toTexas does not have specific rules 15,000 gallons and in both verticalconcerning protection of rainwatersystems from possible contaminationsources; however, to ensure a safe watersupply, underground tanks should belocated at least 50 feet away from animalstables or above-ground application oftreated wastewater. Also, runoff fromtank overflow should not enter septicsystem drainfields. If supplementalhauled water might be needed, tankplacement should also take into Figure 2-5. Two 10,000-gallon fiberglassconsideration accessibility by a water tanks 11
  • cylinder and low-horizontal cylinder Polypropylene tanks do not retain paintconfigurations. well, so it is necessary to find off-the- shelf tanks manufactured with opaqueFiberglass tanks under 1,000 gallons are plastic. The fittings of these tanks areexpensive for their capacity, so aftermarket modifications. Althoughpolypropylene might be preferred. Tanks easy to plumb, the bulkhead fittingsfor potable use should have a USDA- might be subject to leakage.approved food-grade resin lining and thetank should be opaque to inhibit algae Woodgrowth. For aesthetic appeal, a wood tankThe durability of fiberglass tanks has (Figure 2-7) is often a highly desirablebeen tested and proven, weathering the choice for urban and suburban rainwaterelements for years in Texas oil fields. harvesters.They are easily repaired. Wood tanks, similar to wood waterThe fittings on fiberglass tanks are an towers at railroad depots, wereintegral part of the tank, eliminating the historically made of redwood. Modernpotential problem of leaking from an wood tanks are usually of pine, cedar, oraftermarket fitting. cypress wrapped with steel tension cables, and lined with plastic. ForPolypropylene potable use, a food-grade liner must bePolypropylene tanks (Figure 2-6) are used.commonly sold at farm and ranch supplyretailers for all manner of storage uses.Standard tanks must be installed aboveground. For buried installation, speciallyreinforced tanks are necessary towithstand soil expansion andcontraction. They are relativelyinexpensive and durable, lightweight,and long lasting. Polypropylene tanksare available in capacities from 50gallons to 10,000 gallons. Figure 2-7. Installation of a 25,000-gallon Timbertank in Central Texas showing the aesthetic appeal of these wooden tanks These tanks are available in capacities from 700 to 37,000 gallons, and are site- built by skilled technicians. They can be dismantled and reassembled at a different location.Figure 2-6. Low-profile 5,000-gallonpolypropylene tanks 12
  • Metal constructed of stacked rings with sealantGalvanized sheet metal tanks (Figure 2- around the joints. Other types of8) are also an attractive option for the prefabricated concrete tanks include newurban or suburban garden. They are septic tanks, conduit stood on end, andavailable in sizes from 150 to 2,500 concrete blocks. These tanks aregallons, and are lightweight and easy to fabricated off-site and dropped intorelocate. Tanks can be lined for potable place.use. Most tanks are corrugatedgalvanized steel dipped in hot zinc for Concrete may be prone to cracking andcorrosion resistance. They are lined with leaking, especially in underground tanksa food-grade liner, usually polyethylene in clay soil. Leaks can be easily repairedor PVC, or coated on the inside with although the tank may need to beepoxy paint. The paint, which also drained to make the repair. Involving theextends the life of the metal, must be expertise of a structural engineer toFDA- and NSF-approved for potability. determine the size and spacing of reinforcing steel to match the structural loads of a poured-in-place concrete cistern is highly recommended. A product that repairs leaks in concrete tanks, Xypex™, is now also available and approved for potable use.Figure 2-8. Galvanized sheet metaltanks are usually fitted with a food-gradeplastic liner.ConcreteConcrete tanks are either poured in placeor prefabricated (Figure 2-9). They canbe constructed above ground or belowground. Poured-in-place tanks can be Figure 2-9. Concrete tank fabricated from stacking rings of concreteintegrated into new construction under apatio, or a basement, and their placement One possible advantage of concreteis considered permanent. tanks is a desirable taste imparted to theA type of concrete tank familiar to water by calcium in the concrete beingresidents of the Texas Hill Country is dissolved by the slightly acidic 13
  • rainwater. For potable systems, it is Ferrocement structures (Figure 2-10)essential that the interior of the tank be have commonly been used for waterplastered with a high-quality material storage construction in developingapproved for potable use. countries due to low cost and availability of materials. Small cracks and leaks canFerrocement easily be repaired with a mixture ofFerrocement is a low-cost steel and cement and water, which is appliedmortar composite material. For purposes where wet spots appear on the tank’sof this manual, GuniteTM and ShotcreteTM exterior. Because walls can be as thin astype will be classified as ferrocements. 1 inch, a ferrocement tank uses lessBoth involve application of the concrete material than concrete tanks, and thusand mortar under pressure from a gun. can be less expensive. As with poured-Gunite, the dry-gun spray method in in-place concrete construction,which the dry mortar is mixed with assistance from a structural engineer iswater at the nozzle, is familiar for its use encouraged.in swimming pool construction.Shotcrete uses a similar application, but In-ground polypropylenethe mixture is a prepared slurry. Both In-ground tanks are more costly to installmethods are cost-effective for larger for two reasons: the cost of excavationstorage tanks. Tanks made of Gunite and and the cost of a more heavily reinforcedShotcrete consist of an armature made tank needed if the tank is to be buriedfrom a grid of steel reinforcing rods tied more than 2-feet deep in well-drainedtogether with wire around which is soils. Burying a tank in clay is notplaced a wire form with closely spaced recommended because of thelayers of mesh, such as expanded metal expansion/contraction cycles of claylath. A concrete-sand-water mixture is soil. For deeper installation, the walls ofapplied over the form and allowed to poly tanks must be manufactured thickercure. It is important to ensure that the and sometimes an interior bracingferrocement mix does not contain any structure must be added. Tanks aretoxic constituents. Some sources buried for aesthetic or space-savingrecommend painting above-ground tanks reasons.white to reflect the sun’s rays, reduce Table 2-1 provides some values to assistevaporation, and keep the water cool. in planning an appropriate-sized pad and cistern to meet your water needs and your available space. Many owners of rainwater harvesting systems use multiple smaller tanks in sequence to meet their storage capacity needs. This has the advantage of allowing the owner to empty a tank in order to perform maintenance on one tank at a time without losing all water in storage. A summary of cistern materials, theirFigure 2-10. Ferrocement tanks, such as this features, and some words of caution areone, are built in place using a metal armature provided in Table 2-2 to assist theand a sprayed-on cement. prospective harvester in choosing the 14
  • appropriate cistern type. Prior to making rainwater installer is recommended toyour final selection, consulting with an ensure the right choice for yourarchitect, engineer, or professional situation. Table 2-1. Round Cistern Capacity (Gallons) Height (feet) 6-foot Diameter 12-foot Diameter 18-foot Diameter 6 1,269 5,076 11,421 8 1,692 6,768 15,227 10 2,115 8,460 19,034 12 2,538 10,152 22,841 14 2,961 11,844 26,648 16 3,384 13,535 30,455 18 3,807 15,227 34,262 20 4,230 16,919 38,069Rain barrel barrel to a second barrel. A screen trap atOne of the simplest rainwater the water entry point discouragesinstallations, and a practical choice for mosquito breeding. A food-grade plasticurban dwellers, is the 50- to 75-gallon barrel used for bulk liquid storage indrum used as a rain barrel for irrigation restaurants and grocery stores can beof plant beds. Some commercially fitted with a bulkhead fitting and spigotavailable rain barrels are manufactured for garden watering. Other optionswith overflow ports linking the primary include a submersible pump or jet pump. 15
  • Table 2-2. Cistern Types MATERIAL FEATURES CAUTION Plastics Trash cans (20-50 gallon) commercially available; use only new cans inexpensive Fiberglass commercially available; must be sited on smooth, solid, alterable and moveable level footing Polyethylene/polypropylene commercially available; UV-degradable, must be alterable and moveable painted or tinted Metals Steel drums (55-gallon) commercially available; verify prior to use for toxics; alterable and moveable prone to corrosion an rust; Galvanized steel tanks commercially available; possibly corrosion and rust; alterable and moveable must be lined for potable use Concrete and Masonry Ferrocement durable and immoveable potential to crack and fail Stone, concrete block durable and immoveable difficult to maintain Monolithic/Poured-in-place durable and immoveable potential to crack Wood Redwood, fir, cypress attractive, durable, can be expensive disassembled and movedAdapted from Texas Guide to Rainwater Harvesting, Second Edition, Texas Water DevelopmentBoard, 1997. clothes washers, dishwashers, hot-water-Pressure Tanks and Pumps on-demand water heaters – require 20–The laws of physics and the topography 30 psi for proper operation. Even someof most homesteads usually demand a drip irrigation system need 20 psi forpump and pressure tank between water proper irrigation. Water gains 1 psi ofstorage and treatment, and the house or pressure for every 2.31 feet of verticalend use. Standard municipal water rise. So for gravity flow through a 1-inchpressure is 40 pounds per square inch pipe at 40 psi, the storage tanks would(psi) to 60 psi. Many home appliances – 16
  • have to be more than 90 feet above thehouse.Since this elevation separation is rarelypractical or even desirable, two ways toachieve proper household water pressureare (1) a pump, pressure tank, pressureswitch, and check valve (familiar to wellowners), or (2) an on-demand pump.Pumps are designed to push water ratherthan to pull it. Therefore, the systemshould be designed with the pumps atthe same level and as close to the storagetanks as possible.Pump systems draw water from thestorage tanks, pressurize it, and store itin a pressure tank until needed. Thetypical pump-and-pressure tank Figure 2-11. Cistern float filterarrangement consists of a ¾- or 1-horsepower pump, usually a shallow flexible hose, draws water through thewell jet pump or a multistage centrifugal filter.pump, the check valve, and pressureswitch. A one-way check valve between On-demand pumpthe storage tank and the pump prevents The new on-demand pumps eliminatepressurized water from being returned to the need for a pressure tank. Thesethe tank. The pressure switch regulates pumps combine a pump, motor,operation of the pressure tank. The controller, check valve, and pressurepressure tank, with a typical capacity of tank function all in one unit. They are40 gallons, maintains pressure self-priming and are built with a checkthroughout the system. When the valve incorporated into the suction port.pressure tank reaches a preset threshold, Figure 2-12 shows a typical installationthe pressure switch cuts off power to the of an on-demand pump and a 5-micronpump. When there is demand from the fiber filter, 3-micron activated charcoalhousehold, the pressure switch detects filter, and an ultraviolet lamp. Unlikethe drop in pressure in the tank and conventional pumps, on-demand pumpsactivates the pump, drawing more water are designed to activate in response to ainto the pressure tank. demand, eliminating the need, cost, and space of a pressure tank. In addition,The cistern float filter (Figure 2-11) some on-demand pumps are specificallyallows the pump to draw water from the designed to be used with rainwater.storage tank from between 10 and 16inches below the surface. Water at this Treatment and Disinfectionlevel is cleaner and fresher than water Equipmentcloser to the bottom of the tank. Thedevice has a 60-micron filter. An For a nonpotable system used for hoseexternal suction pump, connected via a irrigation, if tree overhang is present, leaf screens on gutters and a roof washer 17
  • diverting 10 gallons for every 1,000square feet of roof is sufficient. If dripirrigation is planned, however, sedimentfiltration may be necessary to preventclogging of emitters. As standards differ,the drip irrigation manufacturer orvendor should be contacted regardingfiltering of water.For potable water systems, treatmentbeyond the leaf screen and roof washeris necessary to remove sediment anddisease-causing pathogens from storedwater. Treatment generally consists offiltration and disinfection processes inseries before distribution to ensurehealth and safety.Cartridge Filters and Ultraviolet (UV)LightThe most popular disinfection array in Figure 2-12. Typical treatment installation ofTexas is two in-line sediment filters – an on-demand pump, 5-micron fiber filter, 3-the 5-micron fiber cartridge filter micron activated charcoal filter, and anfollowed by the 3-micron activated ultraviolet lamp (top).charcoal cartridge filter – followed byultraviolet light. This disinfection set-up another cartridge. The ultraviolet (UV)is placed after the pressure tank or after light must be rated to accommodate thethe on-demand pump. increased flow.It is important to note that cartridge NSF International (National Sanitationfilters must be replaced regularly. Foundation) is an independent testingOtherwise, the filters can actually harbor and certification organization. Filterbacteria and their food supply. The 5- performance can be researched using amicron filter mechanically removes simple search feature by model orsuspended particles and dust. The 3- manufacturer on the NSF website. (Seemicron filter mechanically traps References.) It is best to purchase NSF-microscopic particles while smaller certified equipment.organic molecules are absorbed by the Maintenance of the UV light involvesactivated surface. In theory, activated cleaning of the quartz sleeve. Many UVcharcoal can absorb objectionable odors lights are designed with an integraland tastes, and even some protozoa and wiper unit. Manual cleaning of thecysts (Macomber, 2001). sleeve is not recommended due to theFilters can be arrayed in parallel for possibility of breakage.greater water flow. In other words, two UV lamps are rated in gallons per5-micron fiber filters can be stacked in minute. For single 5-micron and 3-one large cartridge followed by two 3- micron in-line filters, a UV light rated atmicron activated charcoal filters in 12 gallons per minute is sufficient. For 18
  • filters in parallel installation, a UV light water, referred to as “brine,” containingrated for a higher flow is needed. In-line a concentrate of the contaminantsflow restrictors can match flow to the filtered from the feed water, isUV light rating. discharged. The amount of reject water, however, is directly proportional to theUV lights must be replaced after a purity of the feed water. Rainwater, as amaximum of 10,000 hours of operation. purer water source to begin with, wouldSome lights come with alarms warning generate less brine. Reverse osmosisof diminished intensity. membranes must be changed before theyOzone are fouled by contaminants.Chemically, ozone is O3: essentially a Reverse osmosis (RO) equipment formore reactive form of molecular oxygen household use is commercially availablemade up of three atoms of oxygen. from home improvement stores such asOzone acts as a powerful oxidizing agent Lowe’s and Home Depot.to reduce color, to eliminate foul odors,and to reduce total organic carbon in Chlorinationwater. For disinfection purposes, an For those choosing to disinfect withozone generator forces ozone into chlorine, automatic self-dosing systemsstorage tanks through rings or a diffuser are available. A chlorine pump injectsstone. Ozone is unstable and reacts chlorine into the water as it enters thequickly to revert to O2 and dissipates house. In this system, appropriatethrough the atmosphere within 15 contact time is critical to kill bacteria. Aminutes. practical chlorine contact time is usually from 2 minutes to 5 minutes with a freeA rainwater harvesting system owner in chlorine residual of 2 parts per millionFort Worth uses an ozone generator to (ppm). The time length is based on waterkeep the water in his 25,000 gallons of pH, temperature, and amount of bacteria.storage “fresh” by circulating ozone Contact time increases with pH andthrough the five tanks at night. A decreases with temperature. K valuesstandard sprinkler controller switches the (contact times) are shown in Table 3-3.ozone feed from tank to tank.Membrane Filtration (Reverse ReferencesOsmosis and Nanofiltration)Membrane filtration, such as reverse Macomber P. 2001. Guidelines onosmosis and nanofiltration work by rainwater catchment systems forforcing water under high pressure Hawaii. Manoa (HI): College ofthrough a semipermeable membrane to Tropical Agriculture and Humanfilter dissolved solids and salts, both of Resources, University of Hawaii atwhich are in very low concentrations in Manoa. 51 p.rainwater. Membrane processes, NSF International, filter performance,however, have been known empirically www.nsf.org/certified/DWTU/to produce “sweeter” water, perhaps byfiltering out dissolved metals from Radlet J, Radlet P. 2004. Rainwaterplumbing. harvesting design and installation workshop. Boerne (TX): Save theA certain amount of feed water is lost in Rain.any membrane filtration process. Reject 19
  • Rain Water Harvesting and Waste Water collected from rooftops in Bryan and Systems Pty Ltd., College Station, Texas [master www.rainharvesting.com.au thesis]. College Station (TX): Texas A&M University. 180 p.Texas Water Development Board. 1997. Texas guide to rainwater harvesting. Waterfall P. 1998. Harvesting rainwater Austin (TX): Texas Water for landscape use. Tucson (AZ): The Development Board. 58 p. University of Arizona College of Agriculture and Life Sciences. 39 p.Vasudevan L. 2002. A study of biological contaminants in rainwater 20
  • Chapter 3 Water Quality and TreatmentThe raindrop as it falls from the cloud is ranges of 100 ppm to more than 800soft, and is among the cleanest of water ppm.sources. Use of captured rainwater offers The sodium content of some municipalseveral advantages. water ranges from 10 parts per millionRainwater is sodium-free, a benefit for (ppm) to as high as 250 ppm. Rainwaterpersons on restricted sodium diets. intended solely for outdoor irrigation may need no treatment at all except for aIrrigation with captured rainwater screen between the catchment surfacepromotes healthy plant growth. Also, and downspout to keep debris out of thebeing soft water, rainwater extends the tank, and, if the tank is to supply a driplife of appliances as it does not form irrigation system, a small-pore filter atscale or mineral deposits. the tank outlet to keep emitters fromThe environment, the catchment surface, clogging.and the storage tanks affect the qualityof harvested rainwater. With minimal Considerations for the Rainwatertreatment and adequate care of the Harvesting System Ownersystem, however, rainfall can be used as It is worth noting that owners ofpotable water, as well as for irrigation. rainwater harvesting systems who supplyThe falling raindrop acquires slight all domestic needs essentially becomeacidity as it dissolves carbon dioxide and owners of their “water supply systems,”nitrogen. Contaminants captured by the responsible for routine maintenance,rain from the catchment surface and including filter and lamp replacement,storage tanks are of concern for those leak repair, monitoring of water quality,intending to use rainwater as their and system upgrades.potable water source. The catchment The rainwater harvesting system ownerarea may have dust, dirt, fecal matter is responsible for both water supply andfrom birds and small animals, and plant water quality. Maintenance of adebris such as leaves and twigs. rainwater harvesting system is anRainwater intended for domestic potable ongoing periodic duty, to include:use must be treated using appropriatefiltration and disinfection equipment, monitoring tank levels,discussed in Chapter 2, Rainwater cleaning gutters and first-flushHarvesting System Components. devices, repairing leaks,Total dissolved solids (TDS) in repairing and maintaining the system,rainwater, originating from particulate andmatter suspended in the atmosphere, adopting efficient water use practices.range from 2 milligrams per liter (mg/lor ppm)1 to 20 mg/l across Texas,compared with municipal water TDS In addition, owners of potable systems must adopt a regimen of:1 changing out filters regularly, For dilute aqueous solutions mg/l isapproximately equal to ppm because a liter ofwater weighs one kilogram. 21
  • maintaining disinfection equipment, the state, acid rain is not considered a such as cleaning and replacing serious concern in Texas. ultraviolet lamps, and regularly testing water quality. Particulate matter Particulate matter refers to smoke, dust,Water Quality Standards and soot suspended in the air. FineNo federal or state standards exist particulates can be emitted by industrialcurrently for harvested rainwater quality, and residential combustion, vehiclealthough state standards may be exhaust, agricultural controlled burns,developed in 2006. and sandstorms. As rainwater falls through the atmosphere, it canThe latest list of drinking water incorporate these contaminants.requirements can be found on the UnitedStates Environmental Protection Particulate matter is generally not aAgency’s website. (See References.) The concern for rainwater harvesting innext section discusses the potential Texas. However, if you wish, geographicvectors by which contaminants get into data on particulate matter can berainwater. For those intending to harvest accessed at the Air Quality Monitoringrainwater for potable use, the web page of the Texas Commission onmicrobiological contaminants E. coli, Environmental Quality (TCEQ). (SeeCryptosporidium, Giardia lamblia, total References.)coliforms, legionella, fecal coliforms, Chemical compoundsand viruses, are probably of greatest Information on chemical constituentsconcern, and rainwater should be tested can also be found on the TCEQ Airto ensure that none of them are found Quality website. (See References.)(Lye, 2002). County health departmentand city building code staff should also In agricultural areas, rainwater couldbe consulted concerning safe, sanitary have a higher concentration of nitratesoperations and construction of rainwater due to fertilizer residue in theharvesting systems. atmosphere (Thomas and Grenne, 1993). Pesticide residues from crop dusting inFactors Affecting Water Quality agricultural areas may also be present.pH (acidity/alkalinity) Also, dust derived from calcium-richAs a raindrop falls and comes in contact soils in Central and West Texas can addwith the atmosphere, it dissolves 1 mg/l to 2 mg/l of hardness to the water.naturally occurring carbon dioxide to Hard water has a high mineral content,form a weak acid. The resultant pH is usually consisting of calcium andabout 5.7, whereas a pH of 7.0 is neutral. magnesium in the form of carbonates.(A slight buffering using 1 tablespoon of In industrial areas, rainwater samplesbaking soda to 100 gallons of water in can have slightly higher values ofthe tank will neutralize the acid, if suspended solids concentration anddesired. Also, a concrete storage tank turbidity due to the greater amount ofwill impart a slight alkalinity to the particulate matter in the air (Thomas andwater.) While Northeast Texas tends to Grenne, 1993).experience an even lower pH (moreacidic) rainwater than in other parts of 22
  • Catchment surface the valve on the linking pipe betweenWhen rainwater comes in contact with a tanks.catchment surface, it can wash bacteria,molds, algae, fecal matter, other organic Water Treatmentmatter, and/or dust into storage tanks. The cleanliness of the roof in a rainwaterThe longer the span of continuous harvesting system most directly affectsnumber of dry days (days without the quality of the captured water. Therainfall), the more catchment debris is cleaner the roof, the less strain is placedwashed off the roof by a rainfall event on the treatment equipment. It is(Thomas and Grenne, 1993; Vasudevan, advisable that overhanging branches be2002). cut away both to avoid tree litter and to deny access to the roof by rodents andTanks lizards.The more filtering of rainwater prior tothe storage tanks, the less sedimentation For potable systems, a plain galvanizedand introduction of organic matter will roof or a metal roof with epoxy or latexoccur within the tanks. Gutter screens, paint is recommended. Composite orfirst-flush diverters, roof washers, and asphalt shingles are not advisable, asother types of pre-tank filters are toxic components can be leached out bydiscussed in Chapter 2. Sedimentation rainwater. See Chapter 2 for morereduces the capacity of tanks, and the information on roofing material.breakdown of plant and animal matter To improve water quality, severalmay affect the color and taste of water, treatment methods are discussed. It is thein addition to providing nutrients for responsibility of the individual installermicroorganisms. or homeowner to weigh the advantagesMost storage tanks are equipped with and disadvantages of each method formanholes to allow access for cleaning. appropriateness for the individualSediment and sludge can be pumped out situation. A synopsis of treatmentor siphoned out using hose with an techniques is shown in Table 3-1. Ainverted funnel at one end without discussion of the equipment is includeddraining the tank annually. in Chapter 2.Multiple linked tanks allow one tank tobe taken off line for cleaning by closing 23
  • Table 3-1. Treatment Techniques METHOD LOCATION RESULT Treatment Screening Leaf screens and strainers gutters and downspouts prevent leaves and other debris from entering tank Settling Sedimentation within tank settles out particulate matter Activated charcoal before tap removes chlorine* Filtering Roof washer before tank eliminates suspended material In-line/multi-cartridge after pump sieves sediment Activated charcoal after sediment filter removes chlorine, improves taste Slow sand separate tank traps particulate matter Microbiological treatment /Disinfection Boiling/distilling before use kills microorganisms Chemical treatments within tank or at pump (Chlorine or Iodine) (liquid, tablet, or granular) kills microorganisms before activated charcoal filter Ultraviolet light after activated charcoal kills microorganisms filter, before tap Ozonation after activated charcoal kills microorganisms filter, before tap Nanofiltration before use; polymer membrane removes molecules -3 -6 (pores 10 to 10 inch ) Reverse osmosis before use: polymer removes ions (contaminants membrane (pores 10-9 inch) and microorganisms) *Should be used if chlorine has been used as a disinfectant.Adapted from Texas Guide to Rainwater Harvesting, Second Edition, Texas Water DevelopmentBoard, 1997. 24
  • In either case, it is a good idea toChlorination carefully dilute the chlorine source in aChlorination is mentioned here more for bucket of water, and then stir with aits historical value than for practical clean paddle to hasten mixingapplication. Chlorine has been used to (Macomber, 2001). Chlorine contactdisinfect public drinking water since times are show in Table 3-2.1908, and it is still used extensively byrainwater harvesters in Hawaii, the U.S. The use of chlorine for disinfectionVirgin Islands, and in older rainwater presents a few drawbacks. Chlorineharvesting systems in Kentucky and combines with decaying organic matterOhio. Chlorine must be present in a in water to form trihalomethanes. Thisconcentration of 1 ppm to achieve disinfection by-product has been founddisinfection. Liquid chlorine, in the form to cause cancer in laboratory rats. Also,of laundry bleach, usually has 6 percent some users may find the taste and smellavailable sodium hypochlorite. For of chlorine objectionable. To addressdisinfection purposes, 2 fluid ounces this concern, an activated carbon filter(¼ cup) must be added per 1,000 gallons may be used to help remove chlorine.of rainwater. Household bleach products, Chlorine does not kill Giardia orhowever, are not labeled for use in water Cryptosporidium, which are cyststreatment by the Food and Drug protected by their outer shells. PersonsAdministration. A purer form of with weakened or compromised immunechlorine, which comes in solid form for systems are particularly susceptible toswimming pool disinfection, is calcium these maladies. To filter out Giardia andhypochlorite, usually with 75 percent Cryptosporidum cysts, an absolute 1-available chlorine. At that strength, 0.85 micron filter, certified by the NSF, isounces by weight in 1,000 gallons of needed (Macomber, 2001).water would result in a level of 1 ppm. Table 3-2. Contact Time with Chlorine Water Water temperature pH 50 F or 45 F 40 F or warmer colder Contact time in minutes 6.0 3 4 5 6.5 4 5 6 7.0 8 10 12 7.5 12 15 18 8.0 16 20 24UV LightUV light has been used in Europe for common practice in U.S. utilities.disinfection of water since the early Bacteria, virus, and cysts are killed by1900s, and its use has now become exposure to UV light. The water must go 25
  • through sediment filtration before the (See References.) The testing fee isultraviolet light treatment because usually between $15 and $25.pathogens can be shadowed from the UV Homeowners should contact the healthlight by suspended particles in the water. department prior to sample collection toIn water with very high bacterial counts, procure a collection kit and to learn thesome bacteria will be shielded by the proper methods for a grab sample or abodies of other bacteria cells. faucet sample.UV lights are benign: they disinfect Texas Department of State Healthwithout leaving behind any disinfection Services will test for fecal coliforms forby-products. They use minimal power a fee of $20 per sample. (Seefor operation. One should follow References.) A collection kit can bemanufacturer’s recommendations for ordered from TDSHS at (512) 458-7598.replacement of bulbs. Commercial laboratories are listed inTesting telephone Yellow Pages underHarvested rainwater should be tested Laboratories–Analytical & Testing. Forbefore drinking and periodically a fee, the lab will test water forthereafter. Harvested rainwater should pathogens. For an additional fee, labsbe tested both before and after treatment will test for other contaminants, such asto ensure treatment is working. It is metals and pesticides.advisable to test water quarterly at aminimum, if used for drinking. ReferencesHarvested rainwater can be tested by a Lye D. 2002. Health risks associatedcommercial analytical laboratory, the with consumption of untreated watercounty health departments of many from household roof catchmentTexas counties, or the Texas Department systems. Journal of the Americanof Health. Water Resources AssociationBefore capturing rainwater samples for 38(5):1301-1306.testing, contact the testing entity first to Macomber P. 2001. Guidelines onbecome informed of requirements for rainwater catchment systems forcontainer type and cleanliness, sample Hawaii. Manoa (HI): College ofvolume, number of samples needed, and Tropical Agriculture and Humantime constraints for return of the sample. Resources, University of Hawaii atFor instance, for total coliform testing, Manoa. 51 p.water must usually be captured in a Texas Commission on Environmentalsterile container issued by the testing Quality, Air Quality Monitoring,entity and returned within a maximum of www.tceq.state.tx.us/nav/data/pm25.30 to 36 hours. Testing for pH, htmlperformed by commercial analyticallaboratories must be done on site; other Texas Commission on Environmentaltests are less time-critical. Quality, chemical constituents, www.tnrcc.state.tx.us/airquality.htmlA list of county health departments thatwill test for total and fecal coliform can Texas Department of State Healthbe found on the Texas Department of Services, county health departments,State Health Services (TDSHS) website. 26
  • www.dshs.state.tx.us/regions/default. United States Environmental Protection shtm Agency, drinking water requirements, www.epa.gov/safewater/mcl.htmlTexas Department of State Health Services, testing for fecal coliforms, Vasudevan L. 2002. A study of www.dshs.state.tx.us/lab/default.shtm biological contaminants in rainwater collected from rooftops in Bryan andThomas PR, Grenne GR. 1993. College Station, Texas [masters Rainwater quality from different roof thesis]. College Station (TX): Texas catchments. Water Science A&M University. 90 p. Technology (28):290-99. 27
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  • Chapter 4 Water Balance and System SizingThe basic rule for sizing any rainwater sufficient. On the other hand, ifharvesting system is that the volume of rainwater is intended to be the solewater that can be captured and stored source of water for all indoor and(the supply) must equal or exceed the outdoor domestic end uses, a morevolume of water used (the demand). precise reckoning is necessary to ensure adequate supply.The variables of rainfall and waterdemand determine the relationship How Much Water Can Bebetween required catchment area and Captured?storage capacity. In some cases, it maybe necessary to increase catchment In theory, approximately 0.62 gallonssurface area by addition of a rain barn or per square foot of collection surface peroutbuilding to capture enough rainwater inch of rainfall can be collected. Into meet demand. Cistern capacity must practice, however, some rainwater is lostbe sufficient to store enough water to see to first flush, evaporation, splash-out orthe system and its users through the overshoot from the gutters in hard rains,longest expected interval without rain. and possibly leaks. Rough collection surfaces are less efficient at conveyingThe following sections describe ways to water, as water captured in pore spacesdetermine the amount of rainfall, the tends to be lost to evaporation.estimated demand, and how muchstorage capacity is needed to provide an Also impacting achievable efficiency isadequate water supply. the inability of the system to capture all water during intense rainfall events. ForIntended End Use instance, if the flow-through capacity ofThe first decision in rainwater harvesting a filter-type roof washer is exceeded,system design is the intended use of the spillage may occur. Additionally, afterwater. If rainwater is to be used only for storage tanks are full, rainwater can beirrigation, a rough estimate of demand, lost as overflow.supply, and storage capacity may be Figure 4-1. Catchment areas of three different roofs 29
  • Figure 4-2. Average annual precipitationin Texas, in inchesFor planning purposes, therefore, these volume of storage capacity that can beinherent inefficiencies of the system installed.need to be factored into the water supplycalculation. Most installers assume an Collection Surfaceefficiency of 75 percent to 90 percent. The collection surface is the “footprint” of the roof (Figure 4-1). In other words,In most Texas locations, rainfall occurs regardless of the pitch of the roof, theseasonally, requiring a storage capacity effective collection surface is the areasufficient to store water collected during covered by collection surface (lengthrainy times to last through the dry spells. times width of the roof from eave toIn West Texas, total annual rainfall eave and front to rear). Obviously if onlymight not be sufficient to allow a one side of the structure is guttered, onlyresidence with a moderate-sized the area drained by the gutters is used incollection surface to capture sufficient the calculation.water for all domestic use. Someresidences might be constrained by the Rainfall Distributionarea of the collection surfaces or the In Texas, average annual rainfall decreases roughly 1 inch every 15 miles, 30
  • the total available volume of such an event is rarely captured. Another consideration is that most rainfall occurs seasonally; annual rainfall is not evenly distributed throughout the 12 months of the year. The monthly distribution of rainfall is an important factor to consider for sizing a system. Monthly rainfall data for selected Texas cities is given in Appendix B. Monthly RainfallFigure 4-3. Maximum number of dry days Two different estimators of monthly(Krishna, 2003) rainfall are commonly used: average rainfall and median rainfall. Averageas you go from east to west (Figure 4-2), annual rainfall is calculated by taking thefrom 56 inches per year in Beaumont to sum of historical rainfall and dividing byless than 8 inches per year in El Paso. As the number of years of recorded data.one moves westward across the state, the This information is available fromprevalence and severity of droughts must numerous public sources, including thealso be considered. National Climate Data Center website.To ensure a year-round water supply, the (See References.) Median rainfall is thecatchment area and storage capacity amount of rainfall that occurs in themust be sized to meet water demand midpoint of all historic rainfall totals forthrough the longest expected interval any given month. In other words,without rain. For instance, in West historically for the month in question,Texas, the historic longest span of half of the time the rainfall was less thancontinuous dry days has exceeded three the median and half of the time rainfallmonths. For reference purposes, a was more than the median. Mediancontour map of historical maximum values and average rainfall values fornumber of dry days in Texas is shown in representative Texas cities are providedFigure 4-3 (Krishna, 2003). If the in Appendix B.rainwater harvesting system is intended Median rainfall provides for a moreto be the sole water source for a conservative calculation of system sizinghousehold, the designer must size the than average rainfall. The median valuesystem to accommodate the longest for rainfall is usually lower than theanticipated time without rain, or average value since large rainfall eventsotherwise plan for another water source, tend to drive the average value higher. Insuch as a well backup or hauled water. other words, the sum of monthlyAlso, rainfall from high-intensity, short- medians is lower than the annual averageduration rainfall events may be lost to due to the fact that the arithmeticoverflow from storage tanks or splash- average is skewed by high-intensityout from the gutters. Although these rainfall events. For planning purposes,intense rainfall events are considered median monthly rainfall can be used topart of the cumulative annual rainfall, estimate water availability to a 31
  • reasonable degree of certainty (Krishna, The Water Balance Method Using2001). Monthly Demand and SupplyFor example, in the sample calculations One method of determining theat the end of this chapter, the average feasibility of a proposed system is theannual rainfall for Dallas is about 35.0 monthly water balance method. Thisinches, but the sum of the monthly method of calculation is similar tomedians is only 29.3 inches. maintaining a monthly checkbook balance. Starting with an assumedCalculating Storage Capacity volume of water already in the tanks, theOnce the median or average potential for volume captured each month is added torainfall capture is known from rainfall the previous balance and the demand isdata and catchment area, it will be subtracted. The initial volume of waternecessary to calculate storage capacity. in the tanks would be provided byThe decision of whether rainwater will hauling or capturing water prior tobe used for irrigation, potable and withdrawing water from the system. Andomestic use, or both, will dictate water example is presented at the end of thisdemand, and therefore, capacity. chapter.A simple method of roughly estimating Data and calculations can be entered onstorage capacity popular among an electronic spreadsheet to enable theprofessional installers is to size the user to compare different variables ofstorage capacity to meet quarterly catchment area and storage. It isdemand. The system is sized to meet suggested that homeowners experimentestimated demand for a three-month with different variables of storageperiod without rain. Annual estimated capacity and, if applicable, catchmentdemand is divided by four to yield surface to find individual levels ofnecessary storage capacity using this comfort and affordability for catchmentapproach. This approach, however, may size and storage capacity.result in a more expensive system due to As mentioned above:higher storage costs. catchment area and rainfall determineIf a rainwater harvesting system is to be supply, andthe sole water supply, overbuilding demand dictates required storageensures a safety margin. As with many capacity.things in life, it helps to hope for the bestbut plan for the worst. Even when A commitment to conserving water withbudget constraints may not allow the water-saving fixtures, appliances,user to install as much storage capacity practices indoors, and low-water-useas a sizing method may indicate, it is landscaping outdoors is an essentialimportant to provide for an area where component of any rainwater harvestingadditional tanks or cisterns can be system design. Not only is conservationinstalled at a later date when finances good stewardship of natural resources, itpermit. also reduces the costs for storage capacity and related system components. If the amount of rainwater that can be captured – calculated from roof area and rainfall – is adequate or more than 32
  • adequate to meet estimated demand, and efficient water use practices both indoorsmeets the physical constraints of the and outdoors.building design, then storage capacitycan be sized to meet estimated demand. Estimating indoor water demandIf the monthly amount of water that can Indoor water demand is largelybe captured, accounting for dry spells, is unaffected by changes in weather,less than monthly estimated demand, although changes in householdthen additional catchment area or occupancy rates depending upon seasonssupplemental supplies of water (such as and ages of household members, moregroundwater from a well) will need to be water use during the hot summerconsidered. months, and very minor changes in consumption of water due to increases inIn drier areas, no matter how large the temperature may be worth factoring instorage capacity, catchment area may some instances. The results of a study ofneed to be increased with a rain barn or 1,200 single-family homes by theadditional roof area to meet demand. American Water Works AssociationAt the end of this chapter, an example of (AWWA) in 1999 found that the averagea water balance calculation is shown for water conserving households usedthe City of Dallas. approximately 49.6 gallons per person per day (American Water WorksEstimating Demand Association, 1999).A water-conserving household will use Table 4-1 can be used to calculate indoorbetween 25 and 50 gallons per person water demand. Many households useper day. (Note that total gallons per less than the average of 49.6 gallons percapita per day figures published for person found in the 1999 report by themunicipalities divide all the water AWWA, Residential End Uses of Water.distributed by the population, yielding a The water volumes shown in the tablemuch larger amount per capita than assume a water-conserving household,actual domestic consumption.) with water-conserving fixtures and goodHouseholds served previously by a water practices, such as shutting off the waterutility can read monthly demand from while brushing teeth or shaving. Overalltheir meter or water bill to find monthly demand in showers, baths, and faucetdemand for purposes of building a new uses is a function of both time of use andrainwater harvesting system. Divide the rate of flow. Many people do not openmonthly total by the number of people in the flow rate as high as it could bethe house, and the days in the month to finding low or moderate flow rates moreget a daily per capita demand number. comfortable. In estimating demand, measuring flow rates and consumptionWater conservation is covered later in in the household may be worth the effortthis chapter. Households solely to get more accurate estimates.dependent upon rainwater should adopt 33
  • Table 4-1. Estimating Indoor Daily Domestic Demand A. B. C. D. E. Water Assumptions Adjustments to Number of Household consumption from AWWA assumptions persons in monthly using Residential End- (adjust up or household demand conserving Use Study down according fixtures to actual use) A x (B or C )x D x 30Toilets (useonlyappropriatetype)ULFT 1.6 gal/flush 6 flushes/ person/dayDual Flush 1 gal/flush 6 flushes/ liquids person/day 1.6 gal/flush solidsBaths &showersShowerhead 2.2 gal/min 5 minutes/ person/dayBath 50 gal/bath NAFaucets 2.2 5 minutes/(personal gal/faucet/min person/dayhygiene,cooking, andcleaning ofsurfaces)Appliances or uses which are measured on a per-use basis (not a per-person basis):Clothes washer 18–25 gal/load 2.6 loads/weekFront-loading(horizontal-axis)Dishwasher 8 gal/cycle 0.7 cycles/dayMiscellaneousotherTotal One can use Table 4-1 if the designer patterns. The average values in the prefers to incorporate known or expected second column are offered for behavioral habits into the water demand information, but as with all averages, are estimates. The values in the first column subject to wide variation based upon are to be multiplied by variables actual circumstances. An example is reflecting your own household water use dual flush toilets – multiply three flushes 34
  • per day liquid only (1 gpf), and add three designed to use 2.2 gallons per minuteflushes per day for solids (1.6 gpf), (3x1) at 60 psi, or 2.5 gpm at 80 psi (Table+ (3x1.6) = 7.8 gallons multiplied by 3 4-1). Studies have shown that mostpersons = 23.4 gpd household demand x people feel comfortable at less than30 days = 702 gallons per month. The full flow rates, so using the newauthors recommend verifying any fixtures (which are the only ones soldassumptions against the records of in the United States since 1992)historical use from a municipal water bill should provide you with an efficientif available. and comfortable experience.Indoor water conservation Hot water on demand. These wall- mounted units heat water just prior toIndoor domestic water conservation can use, eliminating the waste of waitingbe achieved by a combination of for hot water from the water heaterfixtures, appliances, and water- while cold water is allowed to flowconserving practices. The advantage of down the drain. Hot water loopwater-conserving appliances is that they systems keep hot water continuouslyrequire no change in household routine. circulating to achieve the same goal,Some water-conserving practices need but can use more energy. Another on-user action, such as turning off the water demand unit heats water quickly onlywhile brushing teeth or shaving; washing when activated by a pushbutton,vegetables in a pan rather than under a rather than circulating water through astream; washing only full loads of loop, saving both water and energy. Alaundry and dishes; and keeping a rebate from San Antonio Waterpitcher of water in the refrigerator, rather System (SAWS) is available forthan waiting for cold water to arrive installation of this type of on-demandfrom a faucet. circulation system.Water conservation appliances include: Horizontal-axis (front-loading) clothes Ultralow flush toilets (ULFTs). Since washers. Because clothes are tumbled 1993, only ULFTs with 1.6 gallons through a small volume of water in per flush may be sold in the United the bottom of the drum (rather than States. Older toilets should be washed in a full tub of water), this replaced with the more efficient appliance can save up to half the models. Some of the ULFTs require water of a traditional clothes washer. special early closing flappers to It is also as much as 42 percent more maintain their low-flow rates, so care energy efficient. A list of front- should be taken in purchasing the loading, horizontal-axis clothes correct replacement flapper for washers is maintained by the leaking toilets. If purchasing a new Consortium for Energy Efficiency toilet, those that do not use early online. (See References.) Several closure flappers are recommended. municipal utilities in Texas, including Dual-flush toilets (using less volume City of Austin, SAWS, and Bexar for liquid wastes) are also a good Met, offer rebates for the purchase of choice for a water-wise household. these energy- and water-efficient Faucet aerators and efficient appliances. showerheads. These fixtures are 35
  • Estimating outdoor water demand A recommended general reference forOutdoor water demand peaks in hot, dry water-wise landscaping is Xeriscape:summer. In fact, as much as 60 percent Landscape Water Conservation,of municipal water demand in the publication B-1584, available online.summer is attributable to irrigation. (See References.) Other plant lists and resources are available at the TexasThe water demands of a large turfgrass Master Gardeners’ website. (Seearea almost always preclude the sole use References.) Many municipal waterof harvested rainwater for irrigation. utilities, including those in the cites of ElMany urban dwellers capture rainwater Paso, Houston, Austin, San Antonio, andfor irrigation of vegetable and the Metroplex area have publishedornamental gardens. Because it is free of water-wise landscaping informationsalts and minerals, rainwater promotes tailored to local climate and soilhealthy plant growth. In urban areas, conditionsrainwater harvesters may reduce their It is recommended that rainwaterwater bill by substituting harvested harvesting families install landscapes ofrainwater for municipal water for garden native and adapted plants, and alsoirrigation. ascribe to the seven principles ofFor both the health of landscape plants Xeriscaping. A water-wise landscapeand water use-efficiency, the best way to can be quite attractive, while conservingwater plants is according to their needs. water and demanding less care than aFor most plants adapted to Texas’ garden of non-native or non-adaptedclimate, water stress is visually evident plants.well before plant death. Signs of waterstress include a gray blue tint to leaves,leaf rolling, and in the case of turfgrass, Principles of Water-Wise Landscapinga footprint that does not spring back.Watering infrequently and deeply has 1.Plan and design for water conservation.been shown to promote plant health,waiting until plants need the water helps 2. Create practical turf areas.the water user to be sure that they are 3. Group plants of similar water needsgrowing a healthy landscape. together.For planning purposes, historical 4. Use soil amendments like compost toevapotranspiration can be used to project allow the soil to retain more water.potential water demands.Evapotranspiration is the term for water 5. Use mulches, especially in high anduse by plants, the combination of moderate watering zones, to lessenevaporation from the soil and soil evaporation.transpiration from the plant leaves. An 6. Irrigate efficiently by applying the rightestimated value called potential amount of water at the right time.evapotranspiration is available on theTexas Evapotranspiration website, or 7. Maintain the landscape appropriatelycan be calculated from weather-related by fertilizing, mowing, and pruning.data. (See References.) 36
  • References Krishna H. 2003. An overview of rainwater harvesting systems andAmerican Water Works Association. guidelines in the United States. 1999. Residential end uses of water. Proceedings of the First American Denver (CO): American Water Rainwater Harvesting Conference; Works Association Research 2003 Aug 21-23; Austin (TX). Foundation. 310 p. National Climate Data Center,Consortium for Energy Efficiency, list of www.ncdc.noaa.gov clothes washers, www.cee1.org/resid/seha/rwsh/rwsh- Texas Evapotranspiration Network, main.php3 texaset.tamu.eduKrishna H. 2001. Rainwater catchment Texas Master Gardeners, systems in Texas. Proceedings of the aggiehorticulture.tamu.edu/mastergd/ 10th International Conference on mg.html Rainwater Catchment Systems of the Xeriscape: Landscape Water International Rainwater Catchments Conservation, publication B-1584, Systems Association; 2001 Sep 10- tcebookstore.org 14; Mannheim, Germany. 37
  • Rainwater Harvesting System Sizing Sample Water Balance Calculations for Dallas, TexasTwo methods of determining system sizing are shown below. In the first example, monthlyaverage rainfall data are used, and in the second example, monthly median rainfall data are usedfor calculations. Monthly rainfall data for several locations in Texas are provided in Appendix B.Keep in mind that the basic monthly water balance calculation is Water available (gallons) = Initial volume in storage (gallons) + gallons captured – gallons used.In an especially wet month, gallons in storage + gallons captured may exceed storage capacity;storage capacity could become a limiting factor, or a slightly larger cistern may be considered.Assumptions • Demand of 3,000 gallons/month • Collection efficiency of 85 percent • 0.62 gallons per square foot of roof area per inch of rain • 10,000-gallon storage capacity • 1,000 gallons in storage on January 1 to start out. (The water may have been collected between the time of system completion and new home occupancy, or it may be hauled water; systems designed for irrigation use only should be completed in the fall to collect rainwater during the slow-/non-growth season.) • Irrigation volume is estimated based upon a small ornamental landscape, and limited supplemental irrigation, since this example is used for potable supply.Calculations using Monthly Average Rainfall DataFirst calculate the number of gallons collected in January. Using the average value of 1.91 inches of rain for January in Dallas (from Appendix B), the number of gallons of rainwater that can be expected to be stored in January from a 2,500-square-foot roof assuming 85% collection efficiency is determined from the equation: Rainfall (inches) x roof area x 0.62 gal/sq ft /in. rain x collection efficiency In this example: 1.97in. rainfall x 2,500sq. ft. catchment x 0.62 gallons/in. rain/sq. ft. x 0.85 collection efficiency = 2,595 gallonsTo calculate gallons in storage at the end of each month, add the volume of water already in storage (1,000 gallons in this example) to the gallons collected and subtract the monthly demand. 1,000 + 2,595 – 3,000 = 595 gallons available in storage at the end of JanuaryThis calculation is repeated for each month. To help you follow Table 4-2, please read below:The value in Column E is added to Column F from preceding row and then A is subtracted. Ifcalculated storage amount is zero or less, use zero for the next month. Rainfall exceedingstorage capacity is ignored (water lost). The table shows that a collection surface of 2,500 squarefeet is adequate to meet expected demand (Column F should be more than zero at all times, ifnot the collection area needs to be increased or the monthly demand should be reduced).Calculations using Monthly Median Rainfall DataTable 4-3 shows the results of using monthly median rainfall (Column D), and performing thesame calculations as before. Using monthly median rainfall data is a more conservative method,and is likely to provide a higher reliability than using average rainfall data for system sizing.Homeowners can easily try different values for collection surface and storage capacity using anelectronic spreadsheet, downloadable in Excel format from the Texas Water Development Boardwww.twdb.state.tx.us/assistance/conservation/alternative_technologies/rainwater_harvesting/rain.asp 38
  • Table 4-2. Sample Water Balance Calculations for Dallas, Texas (Using Average Rainfall and a 2,500-square-foot collection surface) A. B. C. D. E. F. Water Irrigation Total Average Rainfall End-of- demand demand demand rainfall collected month (watering by (gallons) (inches) (gallons) storage hose or (1,000 gal. Month bucket) to start) January 3,000 0 3,000 1.97 2,596 595 February 3,000 0 3,000 2.40 3,162 757 March 3,000 150 3,150 2.91 3,834 1,441 April 3,000 150 3,150 3.81 5,020 3,311 May 3,000 150 3,150 5.01 6,601 6,762 June 3,000 150 3,150 3.12 4,111 7,723 July 3,000 150 3,150 2.04 2,688 7,261 August 3,000 150 3,150 2.07 2,727 6,838 September 3,000 150 3,150 2.67 3,518 7,206 October 3,000 150 3,150 3.76 4,954 9,010 November 3,000 0 3,000 2.70 3,557 9,567 December 3,000 0 3,000 2.64 3,478 10,000** Note that there were 44 gallons of overflow in December in this example. A 10,000-gallon cisternappears to be appropriate under the given assumptions. Table 4-3. Sample Water Balance Calculations for Dallas, Texas (Using Median Rainfall and a 2,500-square-foot collection surface) A. B. C. D. E. F. Water Irrigation Total Median Rainfall End-of- demand demand demand rainfall collected month (watering by (gallons) storage hose or (1,000 gal. Month bucket) to start) January 3,000 0 3,000 1.80 2,372 372 February 3,000 0 3,000 2.11 2,780 151 March 3,000 150 3,150 2.36 3,109 111 April 3,000 150 3,150 2.98 3,926 887 May 3,000 150 3,150 4.27 5,626 3,363 June 3,000 150 3,150 2.85 3,755 3,968 July 3,000 150 3,150 1.60 2,108 2,926 August 3,000 150 3,150 1.74 2,292 2,068 September 3,000 150 3,150 2.50 3,294 2,212 October 3,000 150 3,150 2.94 3,873 2,935 November 3,000 0 3,000 2.00 2,635 2,570 December 3,000 0 3,000 2.10 2,767 2,337This table shows that it is critical to start with an initial storage (1,000 gallons), otherwise the cistern mayrun out of water in February/March, under the given assumptions. 39
  • Chapter 5 Rainwater Harvesting GuidelinesNo national standards exist for rainwater Association (ARCSA) is in the processharvesting systems. As a result, efforts of publishing guidelines for potable andabound to give assistance to those nonpotable rainwater harvestingconsidering using rainwater as a water systems. The guidelines will be availablesupply at state and local levels. In Texas on the ARCSA website at www.arcsa-the voluntary approach has been the usa.org.hallmark of water conservation efforts,and a Water Conservation Best Other Voluntary GuidelinesManagement Practices (BMP) Guide A number of University-level programsproduced by the Texas Water have published guidelines that areDevelopment Board (TWDB) in 2004 helpful to rainwater designers andincluded a section on Rainwater planners. Included among them areHarvesting and Condensate Reuse for Texas Cooperative Extension’suse by water providers. (See guidelines and the University ofReferences.) Guidance in other parts of Arizona’s “Harvesting Rainwater forthe country ranges from voluntary Landscape Use,” both of which focus onguidelines such as BMPs to codes and capturing rainwater for outdoorordinances stipulating minimum irrigation. The University of Hawaiistandards for various aspects of College of Tropical Agriculture andrainwater harvesting. The wide variety in Human Resources in Hawaii producedapproaches is summarized in this chapter “Guidelines on Rainwater Catchmentby sharing a few key examples of the Systems in Hawaii,” which hasinitiatives that are available to assist the information for people using rainwaterplanner of a rainwater harvesting system. for potable consumption. (See References.)RWH Best Management Practices These guidelines for potable systemsWater Conservation Implementation recommend that storage tanks beTask Force Guidelines. In 2003 a constructed of non-toxic material such asstatewide Water Conservation steel, fiberglass, redwood, or concrete.Implementation Task Force was Liners used in storage tanks should beappointed by the TWDB under a smooth and of food-grade materiallegislative mandate to develop approved by the U.S. Food and Drugrecommendations for water conservation Administration (Macomber, 2001).for the state of Texas. Best managementpractices reached by a consensus of the Building CodesTask Force address rainwater harvesting In addition to voluntary effort, someand air conditioner condensate in the states and municipalities are choosing toTask Force Water Conservation Best establish rules. Ohio, Kentucky, Hawaii,Management Practices Guide (TWDB, Arizona, New Mexico, Washington,2004). West Virginia, Texas, and the U.S.American Rainwater Catchment Virgin Islands are considering or haveSystems Association. The American developed rules related to rainwaterRainwater Catchment Systems harvesting. 41
  • Rules, ordinances, building codes, and building expansion must have ahomeowner association covenants provision for a self-sustaining waternationwide run the gamut from requiring supply system, either a well or arainwater harvesting systems on new rainwater collection area and cistern.construction to prohibiting tanks as an The rules for private water systems ineyesore. the U.S. Virgin Islands state that newIn Texas, HB 645, passed by the 78th cisterns must have a minimum capacityLegislature in 2003, prevents of 2,500 gallons per dwelling (Virginhomeowners associations from Islands Code, Title 29, Public Planningimplementing new covenants banning and Development).outdoor water-conserving measures such The U.S. Virgin Islands specifies thatas composting, water-efficient cisterns for hotels or multi-familylandscapes, drip irrigation, and rainwater dwellings have a minimum capacity ofharvesting installations. The legislation 10 gallons per square foot of roof areaallows homeowners associations to for buildings of one story, and 15 gallonsrequire screening or shielding to obscure per square foot of roof area for multi-view of the tanks. story buildings, although theThe State of Ohio has the most extensive requirement is waived for buildings withrules on rainwater harvesting in the access to centralized potable waterUnited States, with code on cistern size systems.and material, manhole openings, outlet The City of Portland, Oregon, requires adrains, overflow pipes, fittings, minimum cistern capacity of 1,500couplings, and even roof washers. gallons capable of being filled withOhio’s rules also address disinfection of harvested rainwater or municipal water,private water systems. (See References.) with a reduced pressure backflow prevention device and an air gapCistern Design, Construction, and protecting the municipal supply fromCapacity cross-connection (City of Portland,Cistern design is covered by rules in 2000).some states, often embedded in the rulesfor hauled water storage tanks. In Ohio, Backflow Prevention and Dual-cisterns and stored water storage tanks Use Systemsmust have a smooth interior surface, and The option of “dual-supply” systemsconcrete tanks must be constructed in within a residence – potable harvestedaccordance with ASTM C913, Standard rainwater supplemented with water fromSpecification for Precast Concrete a public water system with appropriateWater and Wastewater Structures. backflow prevention – is an option thatPlastic and fiberglass tank materials and might be explored for residences whichall joints, connections, and sealant must cannot collect enough rainwater.meet NSF/ANSI Standard 61, DrinkingWater System Components. In most Texas locations, rainfall occurs seasonally, requiring a large storageIn the U.S. Virgin Islands, Bermuda, and capacity to hold enough water collectedother Caribbean islands (islands without during rain events to last through the drylarge reservoirs or adequate groundwater spells.reserves), all new construction and even 42
  • Allowing for a connection to the public For instance, Santa Fe County, Newwater supply system could serve to Mexico, passed the precedent-settingpromote harvested rainwater as a regulation requiring rainwater harvestingsupplemental water source to customers systems on new residential oralready connected to the public water commercial structures of 2,500 squaresupply infrastructure. feet and larger. A bill requiring rainwater harvesting systems on all newThis “conjunctive” use would require an construction narrowly missed passage inappropriate backflow prevention device the New Mexico legislature (Darilek,to keep rainwater from entering the 2004; Vitale, 2004)public water supply due to a drop inpressure in the utility’s distribution The City of Tucson, Arizona, hassystem. instituted requirements for water harvesting in its land use code as aThe City of Portland has approved means of providing supplemental watersupplemental use of public utility water for on-site irrigation. In fact, “stormat a residence since 1996. The code water and runoff harvesting toincludes specific guidance for design supplement drip irrigation are requiredand installation of the system. It also elements of the irrigation system forlimits rainwater to nonpotable uses. The both new plantings and preservedPortland Office of Planning and vegetation” (City of Tucson Code,Development publishes a RWH Code Chapter 23).Guide which includes FAQ and therelevant code sections (City of Portland, Water harvesting in Tucson is also2000). intended to help in meeting code requirements for floodplain and erosionThe State of Washington Building Codes hazard management (City of TucsonCouncil in 2002 developed guidelinesfor installation of rainwater harvesting Code, Chapter 26).systems at commercial facilities. They 2005 Rainwater Harvestingare similar to the City of Portland Legislationguidelines mentioned above, but requirea larger cistern size, determined by the The Texas Legislature passed House Billsize of the catchment area, which is (HB) 2430 in May 2005, establishing alimited to roof areas. In 2003, the rainwater harvesting evaluationWashington State Legislature approved a committee to recommend minimum10 percent reduction in stormwater fees water quality guidelines and standardsfor any commercial facility that installed for potable and nonpotable indoor usesa rainwater harvesting system in of rainwater. The committee will alsocompliance with the guidelines recommend treatment methods for(Washington State Legislature, 2003). indoor uses of rainwater, methods by which rainwater harvesting systemsRequired Rainwater Harvesting could be used in conjunction withSystems existing municipal water systems, andPerhaps the most supportive ordinances ways in which that the state can furtherare those requiring rainwater harvesting promote rainwater harvesting. Thein new construction. committee consists of representatives from the Texas Water Development Board, Texas Commission on 43
  • Environmental Quality, Department of NSF International, NSF/ANSI StandardState Health Services, and the Texas 61, Drinking Water SystemSection of the American Water Works Components,Association. The committee will provide www.nsf.org/business/water_distributits recommendations to the Legislature ion/standards.asp?program=WaterDisby December 2006. tributionSys Ohio Department of Health Final Rules,References 3701-28-09 Continuous Disinfection, www.odh.ohio.gov/Rules/Final/ChapASTM. 2004. ASTM C913-98 standard 28/Fr28_lst.htm specification for precast concrete water and wastewater structures. In: Texas Cooperative Extension. 2004. ASTM Book of standards. Rainwater Harvesting. Bryan (TX): Texas Cooperative Extension.City of Portland. 2000. Code guide. Portland (OR): Office of Planning Texas Water Development Board, Water and Development. 18 p. Conservation Best Management Practices Guide, p 96-101,City of Tucson Code, Chapter 23, Land www.twdb.state.tx.us/assistance/cons Use Code, Section 3.7.4.5B. 2004. ervation/TaskForceDocs/WCITFBMCity of Tucson Code, Chapter 26, PGuide.pdf Floodplain and Erosion Hazard Vitale L. 2004 Mar 11. [Personal Management, Section 26-10, communication]. Sante Fe County. Detention/retention systems. 2004. Virgin Islands Code, Title 29, PublicCity of Tucson, Water Harvesting Planning and Development; Chapter Guidance Manual, 5, Building Code; Section 308, Water dot.ci.tucson.az.us/stormwater/educat supply, cisterns, gutters, downspouts, ion/waterharvest.htm wells. 2004.Darilek A. 2004 Mar 11. [Personal Washington State Legislature. 2003 Mar communication]. Office of the New 13. House Bill 2088. Mexico State Engineer. Waterfall P. 1998. Harvesting rainwaterMacomber P. 2001. Guidelines on for landscape use. Tucson (AZ): The rainwater catchment systems for University of Arizona College of Hawaii. Manoa (HI): College of Agriculture and Life Sciences. 39 p. Tropical Agriculture and Human Resources, University of Hawaii at Welsh DF, Welch WC, Duble RL. 2001. Manoa. 51 p. Xeriscape…Landscape Water Conservation. Bryan (TX): Texas Cooperative Extension. 16 p. 44
  • Chapter 6 Cost EstimationDeveloping a budget for a rainwater both potable use and for irrigation. Itharvesting system may be as simple as also has a brief section on comparingadding up the prices for each of the costs with other types of water supply.components and deciding what one can The single largest expense is the storageafford. For households without access to tank, and the cost of the tank is basedreliable groundwater or surface water, upon the size and the material. Table 6-1and too remotely located to hook up to shows a range of potential tank materialsthe existing potable supply and costs per gallon of storage. The sizeinfrastructure, the information in this of storage needed (see Chapter 4, Waterchapter will assist in determining how Balance and System Sizing) and thelarge a system can be installed for a set intended end use of the water will dictatebudget, and the range of costs for an which of the materials are mostideal system. For some, the opportunity appropriate. Costs range from a low ofto provide for all or a portion of their about $0.50 per gallon for largewater needs with rainwater is an exercise fiberglass tanks to up to $4.00 per gallonin comparing the costs with other for welded steel tanks.options to determine which is most cost-effective. This chapter provides some As tank sizes increase, unit costs perinformation on cost ranges for standard gallon of storage decreases.components of rainwater systems for 45
  • Table 6-1. Storage Tank Cost Size CommentsFiberglass $0.50–2.00/gallon 500–20,000 gallons Can last for decades w/out deterioration; easily repaired; can be paintedConcrete $0.30–1.25/gallon Usually 10,000 gallons Risks of cracks and leaks or more but these are easily repaired; immobile; smell and taste of water sometimes affected but the tank can be retrofitted with a plastic linerMetal $0.50–1.50/gallon 150–2,500 gallons Lightweight and easily transported; rusting and leaching of zinc can pose a problem but this can be mitigated with a potable- approved linerPolypropylene $0.35–1.00/gallon 300–10,000 gallons Durable and lightweight; black tanks result in warmer water if tank is exposed to sunlight; clear/translucent tanks foster algae growthWood $2.00/gallon 700–50,000 gallons Esthetically pleasing, sometimes preferable in public areas and residential neighborhoodsPolyethylene $0.74–1.67/gallon 300–5,000 gallonsWelded Steel $0.80–$4.00/gallon 30,000–1 million gallonsRain Barrel $100 55–100 gallons Avoid barrels that contain toxic materials; add screens for mosquitoesGutters and downspouts (Table 6-2) are approximately the same cost. For thoseneeded to collect the water and route it desiring professionally installedto the tank. Two types of gutters are materials, costs range from $3.50 to $12available for the “do-it-yourselfers”: per foot of gutter, including materialsvinyl and plastic, which are available for and installation, in 2004. 46
  • Table 6-2. Gutters Cost Comments Vinyl $.30/foot Easy to install and attach to PVC trunk lines Plastic $.30/foot Leaking, warping and breaking are common problems Aluminum $3.50-6.25/foot Must be professionally installed Galvalume $9-12/foot Mixture of aluminum and galvanized steel; must be professionally installedSome method of discarding the first The roof washer, placed just ahead of theflush of rain from the roof is necessary storage tank, usually consists of a tankto remove debris. The simplest method with leaf strainers and a filter. Ais a vertical PVC standpipe, which fills commercially available model has awith the first flush of water from the series of baffles and a 30-micron filter.roof, then routes the balance of water tothe tank. 47
  • Table 6-3. Roof Washers Cost Maintenance CommentsBox Washer $400-800 Clean the filter after Neglecting to clean every substantial rain the filter will result in restricted or blocked water flow and may become a source or contaminationPost Filtering w/ Sand $150-500 Occasionally Susceptible toFilter backwash the filter freezing; a larger filter is bestSmart-Valve $50 for kit Occasional cleaning Device installed in aRainwater Diverter diversion pipe toKit make it self-flushing and prevent debris contamination; resets automaticallyRoof washers consist of a tank, usually Table 6-4 shows the ranges for pumpbetween 30- and 50-gallon capacity, costs including pressure tanks. Demand-with leaf strainers and a filter. A roof activated pumps such as Grundfos maywasher is a critical component of potable not require a pressure tank, and can oftensystems and is also needed to filter small provide enough water to meet a home’sparticles to avoid clogging drip irrigation demand for instantaneous flow. Carefulemitters. A wide range of equipment is thought should be given to theavailable with different flow capacity possibility of multiple simultaneousand maintenance requirements. In Table demands upon the system in determining6-3 a list of different equipment used to the appropriate size pump. The range forintercept and pre-filter the water shows a pump costs runs from $385 for the low-range of costs from $50 to more than end tankless pump, to more than $1,000$800. It is important that the rainwater for the combined price of a high-endharvester pick a roof washer that is pump and pressure tank.adequate for the size of collection area. 48
  • Table 6-4. Pumps and Pressure Tanks Cost Comments Grundfos MQ Water Supply $385-600 Does not require a separate System pressure tank Shallow Well Jet Pump or $300-600 These require a separate Multi-Stage Centrifugal Pump pressure tank Pressure Tank $200-500 Galvanized tanks are cheaper than bladder tanks but often become waterlogged, and this will wear out the pump more rapidlyFor those planning a potable system, or widely depending upon intended end-if a drip irrigation system is used, some use, the desired water quality, andsort of filtration is necessary. Rainwater preferences of the user. As shown inharvesting suppliers can assist the end Table 6-5, combined filtration/user in purchasing the right equipment disinfection costs can cost up to $1,000for his/her needs and the expected or more. Chapter 2, Rainwaterdemand. Harvesting System Components, will assist you in choosing the right filtrationIt is important for the end user intending and/or disinfection equipment for yourto use rainwater for potable supply toinclude disinfection among the water system.treatment components. The costs vary 49
  • Table 6-5. Filtering/Disinfection Cost Maintenance Effectiveness CommentsCartridge Filter $20-60 Filter must be Removes A disinfection changed particles >3 treatment is also regularly microns recommendedReverse Osmosis $400-1500 Change filter Removes A disinfectionFilter when clogged particles >0.001 treatment is also (depends on the microns recommended turbidity)UV Light $350-1000; $80 Change UV bulb Disinfects Water must beDisinfection to replace UV every 10,000 filtered water filtered prior to bulb hours or 14 provided there exposure for months; the are <1,000 maximum protective cover coliforms per effectiveness must be cleaned 100 milliliter regularlyOzone $700-2600 Effectiveness Less effective in Requires a pumpDisinfection must be high turbidity, to circulate the monitored with can be improved ozone molecules frequent testing with pre-filtering or an in-line monitor ($1,200 or more)Chlorine $1/month manual Monthly dose High turbidity ExcessiveDisinfection dose or a $600- applied manually requires a higher chlorination may $3000 automatic concentration or be linked to self-dosing prolonged negative health system exposure but this impacts. can be mitigated by pre-filtering recommendations for regularOperating Costs maintenance. But proper operation andThere are also operating costs that maintenance of the system does add toshould be considered as you prepare total costs.your budget. As with any watertreatment system, the cleaner the water Filter cartridges should be replaced perneeds to be, the greater the effort manufacturer’s specifications, basedrequired to maintain the system. upon the rate of water use.Fortunately, with filter cartridges, this Some of the operating costs and timejust means regular replacement of the expenditures necessary for systemcartridges, and with the disinfection maintenance are regularly cleaningsystem, following the manufacturers’ gutters and roof washers, checking the 50
  • system for leaks by monitoring water with no guarantee of hitting a reliablelevels, and paying close attention to source of water. The deeper the well, thewater use rates to determine if an more expensive the effort will be. Also,invisible leak has sprung. Although the well water can have very high TDS“do-it-yourselfers” can handle all of levels in some aquifers, resulting inthese tasks with little added financial “hard” water. Rainwater is naturally softburden, the time for regular maintenance and has become a preferred option inand operation must be set aside to some parts of rural central Texas withoperate a successful system. costs lower than or equal to those of drilling a well, and reliability highComparing to Other Sources of enough to justify reliance on weatherWater patterns, rather than on an aquifer’sIn some areas of Texas the cost of water quality and quantity.drilling a well can be as high as $20,000 51
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  • Chapter 7 Financial and Other IncentivesFinancial incentives and tax exemptions regulations did not raise a facility’sencourage the installation of rainwater property taxes, by adding Section 11.31harvesting systems. The Texas to Chapter 11, and Section 26.045 toLegislature has passed bills, and some Chapter 26 of the Texas Tax Code.local taxing entities have adopted rules The Texas Commission onthat provide tax exemptions for Environmental Quality (TCEQ)rainwater harvesting systems. A few established procedures and mechanismspublic utilities have implemented rebate for use determination under Texasprograms and rain barrel distribution Administrative Code (TAC) Title 30,events that encourage rainwater Chapter 17.harvesting by residential, commercial,and industrial customers. In addition to To qualify for the property taxfinancial incentives, performance exemption, (1) a facility must firstcontracting provisions in state code can receive a determination from the TCEQbe used to encourage installation of that the property is used for pollutionrainwater harvesting systems. This control purposes, and (2) the applicantchapter includes a brief description of then submits this use determination tomethods for determining the appropriate the local tax appraisal district to obtainsize of an incentive by local the property tax exemption.governments. The Application and Instructions for UseIn addition to financial incentives, Determination for Pollution Controladministrative contracting rules for state Property and Predetermined Equipmentand local governments encourage the use List, as well as instructions for applyingof rainwater harvesting as an alternative for Property Tax Exemptions forwater source in Texas. Pollution Control Property, are downloadable from the TCEQ website.Tax Exemptions (See References.)Property tax exemption for commercial Property tax exemptions extended (State-installations (State-wide exemption) wide)A constitutional amendment passed as Passed in 2001 by the 77th TexasProposition 2 by Texas voters in Legislature, Senate Bill 2 amendedNovember 1993 exempted pollution Section 11.32 of the Texas Tax Code tocontrol equipment, including water- allow taxing units of government theconserving equipment at nonresidential option to exempt from taxation all orbuildings, from property taxes. part of the assessed value of the propertyRainwater harvesting equipment at on which water conservationcommercial installations is considered modifications have been made. Thewater-conserving equipment. The intent taxing entity designates by ordinance orof this amendment to Article VIII of the law the list of eligible waterTexas Constitution was to ensure that conservation initiatives, which maycapital expenditures undertaken to include rainwater harvesting systems.comply with environmental rules and 53
  • rainwater harvesting equipment orCounty property tax exemptions supplies, water recycling and reuseHomeowners planning to install equipment or supplies, or otherrainwater harvesting systems should equipment.”check with their respective countyappraisal districts for guidance on An application for sales tax exemption isexemption from county property taxes. included as Appendix D, or can beLinks to some county appraisal districts, downloaded from the Office of the Stateas well as the Office of the State Comptroller. (See References.)Comptroller’s Application for WaterConservation Initiatives Property Tax Municipal IncentivesExemption, can be found online. (See In addition to tax exemptions, two TexasReferences.) cities offer financial incentives in the form of rebates and discounts to theirHays County is one of the fastest- customers who install rainwatergrowing counties in Texas, and is also harvesting and condensate recoverythe county with the most rapidly systems.increasing number of new rainwaterharvesting installations in the state. Hays City of Austin Rainwater HarvestingCounty encourages rainwater harvesting Programswith a $100 rebate on the development The City of Austin Water Conservationapplication fee. Department promotes both residential and commercial/industrial rainwaterFor rainwater harvesting systems serving harvesting. (See References.) The Cityas the sole source of water for a of Austin sells 75-gallon polyethyleneresidence, Hays County grants a rain barrels to its customers below cost,property tax exemption from county at $60 each, up to four rain barrels pertaxes for the value of the rainwater customer. City of Austin customers whoharvesting system. Guidelines for purchase their own rain barrels arerainwater harvesting benefits and eligible for a $30 rebate.qualification can be found at the HaysCounty website. (See References.) Customers may also receive a rebate of up to $500 on the cost of installing a pre-Homeowners in other parts of the state approved rainwater harvesting system.should consider approaching their local The rebate application includes agovernment to see if such a property tax formula to calculate optimum tank sizeexemption could be passed in their and a list of area suppliers andlocale. installation contractors. (SeeSales Tax Exemption (State-wide) References.)Senate Bill 2 exempts rainwater Commercial entities may be eligible forharvesting equipment and supplies from as much as a $40,000 rebate against thesales tax. Senate Bill 2 amended cost of installing new equipment andSubchapter H of the Tax Code by adding processes to save water under theSection 151.355, which states: Commercial Incentive Program. (See “Water-related exemptions. The References.) following are exempted from taxes New commercial or industrial sites that imposed by this chapter: (1) develop capacity to store sufficient water 54
  • on-site for landscape irrigation may be Best Management Practices Guide (p.able to receive an exemption from 118 to 130), gives an example and theinstalling an irrigation meter. steps in calculating the net present value of conserved water.San Antonio Water System Large-ScaleRetrofit This approach requires the utility toRainwater harvesting projects are estimate the potential for water savingseligible for up to a 50-percent rebate due to rainwater harvesting systemsunder San Antonio Water System’s installed and the likely number of(SAWS) Large-Scale Retrofit Rebate participants in a program.Program. (See References.) SAWS willrebate up to 50 percent of the installed Rainwater Harvesting at Statecost of new water-saving equipment, Facilitiesincluding rainwater harvesting systems, In 2003, the 78th Texas Legislature,to its commercial, industrial, and second session, passed HB9, whichinstitutional customers. Rebates are encourages rainwater harvesting andcalculated by multiplying acre-feet of water recycling at state facilities. Thewater conserved by a set value of bill requires that the Texas Building and$200/acre-foot. Equipment and projects Procurement Commission appoint a taskmust remain in service for 10 years. The force charged with developing designwater savings project is sub-metered, recommendations to encourageand water use data before and after the rainwater harvesting and water recyclingretrofit are submitted to SAWS to at state facilities built with appropriateddetermine if conservation goals are met. money.To qualify for the rebate, an engineering The intent of HB9 is to promote theproposal and the results of a professional conservation of energy and water at statewater audit showing expected savings buildings. The bill requires that before aare submitted. state agency may use appropriatedThe rebate shortens the return on money to make a capital expenditure forinvestment period, giving an incentive to a state building, the state agency mustindustry to undertake water-conserving determine whether the expenditure couldprojects. be financed with money generated by a utility cost-savings contract.Determining How Much of a FinancialIncentive a Utility May Wish to Offer If it is determined to be not practicableTo determine whether a municipal utility to finance construction with utility costshould consider offering a rebate or savings, rainwater harvesting and waterfinancial incentive to stimulate the use of recycling are encouraged by HB9.rainwater harvesting, benefits and costs In addition the Texas Education Codemust be presented on an economic basis. (Section 61.0591) provides an incentiveThis is most easily accomplished by to institutes of higher education forcondensing the factors into terms of achieving goals set by the Texas Higherdollars per acre-foot ($/AF) and Education Coordinating Board (THECB)comparing that to the cost of building a including:new water supply project. Thespreadsheet included in the TWDB’sReport No. 362, Water Conservation 55
  • “energy conservation and water amendments that increase the water- conservation, rainwater harvesting, holding capacity of the soil, and water reuse.” including compost.”The code states that not less than 10 “rainwater harvesting equipment andpercent of THECB total base funding equipment to make use of waterwill be devoted to incentive funding. collected as part of a stormwater system installed for water qualityPerformance Contracting control.”Another means of encouraging the “equipment needed to capture waterinstallation of water- or energy-efficient from nonconventional, alternateequipment is to pay for the equipment sources, including air-conditioningthrough the savings in utility bills. This condensate or graywater, formethod of financing water conservation nonpotable uses, and meteringhas been used by commercial and equipment needed to segregate waterindustrial consumers, and is written into use in order to identify waterstate code for government buildings in conservation opportunities or verifyseveral locations. water savings.”The Texas Education Code (Chapter Performance contracts serve as a win-44.901 and Chapter 51.927), the Texas win opportunity for school districts andLocal Government Code (Chapter institutes of higher education to effect302.004), and the State Government improvements on facilities for water-Code (Chapter 2166.406) allow public and energy-conservation withoutschools, institutes of higher education, incurring net construction costs.state building facilities, and localgovernments to enter into performance The State Energy Conservation Office,contracts. Performance contracting in Suggested Water Efficiencyallows a facility to finance water- and Guidelines for Buildings and Equipmentenergy-saving retrofits with money at Texas State Facilities, recommendssaved by the reduced utility expenditures that use of alterative water sources bemade possible by the retrofit. In other explored for landscape irrigation use.words, the water- and energy-conserving (See References.) Suggested watermeasures pay for themselves within the sources include captured stormwater orcontracted period. More information on rainwater, air-conditioner condensate,performance contracting can be found on water from basement sump pumpthe State Energy Conservation Office discharge, and other sources, inwebsite. (See References.) accordance with local plumbing codes.Following are descriptions of alternativewater sources that are eligible for Referencesperformance contracts: City of Austin Water Conservation “landscaping measures that reduce Department, watering demands and capture and www.ci.austin.tx.us/watercon/ hold applied water and rainfall, including: (a) landscape contouring, City of Austin Water Conservation including the use of berms, swales, Department, commercial process and terraces; and (b) the use of soil evaluations and rebates, 56
  • www.ci.austin.tx.us/watercon/comme www.tnrcc.state.tx.us/exec/chiefeng/p rcial.htm rop2/0611.docCity of Austin Water Conservation Texas county appraisal districts, Department, rainbarrel rebate, www.texascad.com www.ci.austin.tx.us/watercon/rainwat Texas Statutes Tax Code, er.htm www.capitol.state.tx.us/statutes/tx.tocHays County, rainwater harvesting .htm benefits and qualification, Texas Water Development Board, Water www.co.hays.tx.us/departments/envir Conservation Best Management ohealth/forms.php Practices Guide, p 96-101,Office of the State Comptroller, www.twdb.state.tx.us/assistance/cons application for sales tax exemption, ervation/TaskForceDocs/WCITFBM www.window.state.tx.us/taxinfo/taxf PGuide.pdf orms/01-3392.pdfOffice of the State Comptroller, application for water conservation initiatives property tax exemption, www.window.state.tx.us/taxinfo/taxf orms/50-270.pdfSan Antonio Water System, large-scale retrofit rebate program, www.saws.org/conservation/commer cial/retrofit.shtmlState Energy Conservation Office, www.seco.cpa.state.tx.us/sa_perform contract.htmState Energy Conservation Office, Suggested Water Efficiency Guidelines for Buildings and Equipment at Texas State Facilities, www.seco.cpa.state.tx.us/waterconser vation.pdfTexas Commission on Environmental Quality, application and instructions for use determination for pollution control property and predetermined equipment list, www.tnrcc.state.tx.us/exec/chiefeng/p rop2/guidance.pdfTexas Commission on Environmental Quality, property tax exemptions for pollution control property, 57
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  • Appendix A ReferencesASTM. 2004. ASTM C913-98 standard City of Tucson Code. 2004. Chapter 26, specification for precast concrete Floodplain and Erosion Hazard Area water and wastewater structures. In: Regulations, Section 26-10, ASTM Book of standards. Detention/retention systems.American Rainwater Catchment Systems College of Tropical Agriculture and Association. 2003. First American Human Resources. 2000. Rainwater rainwater harvesting conference catchment systems. Manoa (HI): proceedings. Austin (TX). 2003 Aug University of Hawaii at Manoa. 4 p. 21-22. County of Hawaii. Undated. GuidelinesAmerican Water Works Association. for owners of rain catchment water 1999. Residential end uses of water. systems. Hilo (HI): County of Denver (CO): American Water Hawaii. 5 p. Works Association Research Darilek A. 2004 Mar 11. [Personal Foundation. 310 p. communication]. Office of the NewBanks S, Heinichen R. 2004. Rainwater Mexico State Engineer. collection for the mechanically Darrow K, Saxenian M. 1986. challenged. Dripping Springs (TX): Appropriate technology sourcebook: Tank Town Publishing. 108 p. a guide to practical books for villageCampbell S. 1983. Home water supply: and small community technology. how to find, filter, store, and conserve Stanford (CA): Volunteers in Asia. it. Charlotte (VT): Garden Way 800 p. Publishing. 240 p. Frasier G. 1974. Water harvestingCity of Albuquerque. 1999. Rainwater symposium proceedings. Phoenix harvesting: supply from the sky. (AZ). 1974 Mar 26-28. Albuquerque (NM): Water Use and Gould J, Nissen-Petersen E. 1999. Conservation Bureau. 32 p. Rainwater catchment systems forCity of Albuquerque. 2000. A waterwise domestic rain: design construction guide to rainwater harvesting. and implementation. London: Albuquerque (NM): Water Use and Intermediate Technology Conservation Bureau. 4 p. Publications. 335 p.City of Austin. 1995. Sustainable Kinkade-Levario H. 2004. Forgotten building sourcebook. Austin (TX): rain. City of Austin Environmental and Krishna H. 2001. Rainwater catchment Conservation Services Department. systems in Texas. Proceedings of the 400 p. 10th International Conference onCity of Portland. 2000. Code guide. Rainwater Catchment Systems of the Portland (OR): Office of Planning International Rainwater Catchments and Development. 18 p. Systems Association; 2001 Sep 10- 14; Mannheim, Germany. A1
  • Krishna H. 2003. An overview of Radlet J, Radlet P. 2004. Rainwater rainwater harvesting systems and harvesting design and installation guidelines in the United States. workshop. Boerne (TX): Save the Proceedings of the First American Rain. Rainwater Harvesting Conference; Speidel DH, Ruesdisili LC, Agnew AF. 2003 Aug 21-23; Austin (TX). 1987. Perspectives on water uses andLye D. 1992. Microbiology of rainwater abuses. New York (NY): Oxford cistern systems: a review. Journal of University Press. 400 p. Environmental Science and Health Spence CC. 1980. The rainmakers: A27(8):2123-2166. American pluviculture to World WarLye D. 2002. Health risks associated II. Lincoln (NE): University of with consumption of untreated water Nebraska Press. 181 p. from household roof catchment Steadman P. 1975. Energy, environment systems. Journal of the American and building. New York (NY): Water Resources Association Cambridge University Press. 287 p. 38(5):1301-1306. Steward JC. 1990. Drinking waterMacomber P. 2001. Guidelines on hazards: how to know if there are rainwater catchment systems for toxic chemicals in your water and Hawaii. Manoa (HI): College of what to do if there are. Hiram (OH): Tropical Agriculture and Human EnviroGraphics. Resources, University of Hawaii at Manoa. 51 p. Still GT, Thomas TH. 2003. Sizing and optimally locating guttering forMorgan D, Travathan S. 2002. Storm rainwater harvesting. Proceedings of water as a resource: how to harvest the 11th International Conference on and protect a dryland treasure. Santa Rainwater Catchment Systems; 2003 Fe (NM): City of Santa Fe. 24 p. Aug 25-29; Mexico City (MX).National Academy of Sciences. 1974. Thomas PR, Grenne GR. 1993. More water for arid lands. Rainwater quality from different roof Washington (DC): National Academy catchments. Water Science of Sciences. 149 p. Technology (28):290-99.National Park Service. 1993. Guiding Texas Cooperative Extension. 2004. principles of sustainable Rainwater Harvesting. Bryan (TX): development. Denver (CO): Texas Cooperative Extension. Government Printing Office. Texas Water Development Board. 1997.Pacey A, Cullis A. 1986. Rainwater Texas guide to rainwater harvesting. harvesting: the collection of rainwater Austin (TX): Texas Water and runoff in rural areas. London Development Board. 58 p. (UK): Intermediate Technology Productions. 216 p. Texas Water Development Board. 2002. Water for Texas – 2002. Austin (TX):Phillips A. 2003. City of Tucson water Texas Water Development Board. harvesting guidance manual. Tucson 155 p. (AZ): City of Tucson. 36 p. A2
  • Vasudevan L. 2002. A study of www.ci.austin.tx.us/watercon/rainwat biological contaminants in rainwater er.htm collected from rooftops in Bryan and City of Austin Green Builder Program, College Station, Texas [masters www.ci.austin.tx.us/greenbuilder/ thesis]. College Station (TX): Texas A&M University. 180 p. City of Tucson. 2003. Water Harvesting Guidance Manual,Virgin Islands Code. 2004. Title 29, dot.ci.tucson.az.us/stormwater/educat Public Planning and Development; ion/waterharvest.htm Chapter 5, Building Code; Section 308, Water supply, cisterns, gutters, City of Tucson Code. 2004. Chapter 23, downspouts, wells. Land Use Code, Section 3.7.4.5B, Use of Water,Vitale L. 2004 Mar 11. [Personal www.tucsonaz.gov/planning/luc/luc.h communication]. Sante Fe County. tmWaterfall P. 1998. Harvesting rainwater Consortium for Energy Efficiency, list of for landscape use. Tucson (AZ): The clothes washers, University of Arizona College of www.cee1.org/resid/seha/rwsh/rwsh- Agriculture and Life Sciences. 39 p. main.php3Washington State Legislature. 2003 Mar Green Builders, www.greenbuilder.com 13. House Bill 2088. Hays County, guidelines for rainwaterWelsh DF, Welch WC, Duble RL. 2001. harvesting benefits and qualifications, Xeriscape…Landscape Water www.co.hays.tx.us/departments/envir Conservation. Bryan (TX): Texas ohealth/forms.php Cooperative Extension. 16 p. International Rainwater Catchment Systems Association, www.ircsa.orgWebsites National Climate Data Center,American Rainwater Catchment Systems www.ncdc.noaa.gov Association, www.arcsa-usa.org National Oceanographic andApplication for Water Conservation Atmospheric Administration, Initiatives Property Tax Exemption, www.noaa.gov www.window.state.tx.us/taxinfo/taxf NSF International, filter performance, orms/50-170.pdf www.nsf.org/certified/DWTU/City of Austin Water Conservation NSF International, NSF/ANSI Standard Department, 61, Drinking Water System www.ci.austin.tx.us/watercon/ Components,City of Austin Water Conservation www.nsf.org/business/water_distribut Department, commercial process ion/standards.asp?program=WaterDis evaluations and rebates, tributionSys www.ci.austin.tx.us/watercon/comme Office of Arid Land Studies Desert rcial.htm Research Unit, Casa del Agua,City of Austin Water Conservation www.ag.arizona.edu/OALS/oals/dru/ Department, rainbarrel rebate, casadelagua.html A3
  • Office of the State Comptroller, for use determination for pollution application for sales tax exemption, control property and predetermined www.window.state.tx.us/taxinfo/taxf equipment list, orms/01-3392.pdf www.tnrcc.state.tx.us/exec/chiefeng/p rop2/guidance.pdfOffice of the State Comptroller, application for water conservation Texas Commission on Environmental initiatives property tax exemption, Quality, chemical constituents, www.window.state.tx.us/taxinfo/taxf www.tnrcc.state.tx.us/airquality.html orms/50-270.pdf Texas Commission on EnvironmentalOhio Department of Health Final Rules, Quality, property tax exemptions for 3701-28-09 Continuous Disinfection, pollution control property, www.odh.ohio.gov/Rules/Final/Chap www.tnrcc.state.tx.us/exec/chiefeng/p 28/Fr28_lst.htm rop2/0611.docOrganization of American States, Texas county appraisal districts, Rainwater Harvesting from Rooftop www.texascad.com Catchments, Texas Department of State Health www.oas.org/usde/publications/Unit/ Services, county health departments, oea59e/ch10.htm www.dshs.state.tx.us/regions/default.Rain Water Harvesting and Waste Water shtm Systems Pty Ltd., Texas Department of State Health www.rainharvesting.com.au Services, testing for fecal coliforms,San Antonio Water System, large-scale www.dshs.state.tx.us/lab/default.shtm retrofit rebate program, Texas Evapotranspiration, www.saws.org/conservation/commer texaset.tamu.edu cial/retrofit.shtml Texas Legal Directory, county appraisalState Energy Conservation Office, districts, www.texascad.com www.seco.cpa.state.tx.us/sa_perform contract.htm Texas Legislature Online, www.capitol.state.tx.us/State Energy Conservation Office, Suggested Water Efficiency Texas Master Gardeners, Guidelines for Buildings and aggiehorticulture.tamu.edu/mastergd/ Equipment at Texas State Facilities, mg.html www.seco.cpa.state.tx.us/waterconser Texas Statutes Education Code, vation.pdf www.capitol.state.tx.us/statutes/ed.toTexas Administrative Code, c.htm www.sos.state.tx.us/tac/ Texas Statutes Local Government Code,Texas Commission on Environmental www.capitol.state.tx.us/statutes/lg.toc Quality, Air Quality Monitoring, .htm www.tceq.state.tx.us/nav/data/pm25. Texas Statutes Tax Code, html www.capitol.state.tx.us/statutes/tx.tocTexas Commission on Environmental .htm Quality, application and instructions A4
  • Texas Water Development Board, Water www.twdb.state.tx.us/assistance/cons Conservation Best Management ervation/consindex.asp Practices Guide, p 96-101, United States Environmental Protection www.twdb.state.tx.us/assistance/cons Agency, drinking water requirements, ervation/TaskForceDocs/WCITFBM www.epa.gov/safewater/mcl.html PGuide.pdf United States Environmental ProtectionTexas Water Development Board Agency Safe Drinking Water Act, Conservation, www.epa.gov/safewater/sdwa/sdwa.htm A5
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  • Appendix B Rainfall Data The following data are provided for representative Texas cities in various geographical areas to assist in assessing the optimal storage size for a particular rainwater harvesting system. Each rainwater harvesting system designer should assess the variables of water demand, rainfall, catchment surface area, storage capacity, and risk tolerance when designing a rainwater harvesting system, especially one intended to be the sole water source.Abilene Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.00 0.00 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Maximum 4.35 3.60 5.16 6.80 13.17 9.60 7.52 8.18 11.03 10.68 4.60 6.28Median 0.81 0.73 0.90 1.88 2.47 2.30 1.69 1.62 2.25 2.09 0.94 0.77Average 1.00 1.05 1.17 2.05 3.22 2.90 2.03 2.40 2.71 2.56 1.24 1.03Average annual rainfall 23.36Amarillo Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.00 0.00 0.00 0.00 0.04 0.01 0.10 0.28 0.03 0.00 0.00 0.00Maximum 2.33 1.83 4.01 5.84 9.81 10.73 7.59 7.55 5.02 6.34 2.26 4.52Median 0.33 0.42 0.58 0.86 2.45 3.08 2.59 2.79 1.61 0.97 0.43 0.35Average 0.52 0.55 0.93 1.18 2.67 3.40 2.80 2.93 1.84 1.44 0.59 0.53Average annual rainfall 19.39Austin Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.09 0.00 0.00 0.00Maximum 9.21 6.56 6.03 9.93 9.98 14.96 10.54 8.90 7.44 12.31 7.95 14.16Median 1.27 2.30 1.73 2.20 3.68 2.89 1.15 1.27 2.98 2.82 1.88 1.42Average 1.77 2.37 1.90 2.83 4.33 3.54 1.73 2.18 3.17 3.63 2.25 2.26Average annual rainfall 31.96Brady Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.00 0.10 0.00 0.00 0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00Maximum 6.40 5.30 4.30 6.02 8.00 7.70 13.55 11.30 9.45 7.04 10.40 7.90Median 0.60 1.26 0.90 1.78 3.10 1.87 0.85 1.34 2.40 1.70 1.10 0.70Average 1.03 1.50 1.26 2.07 3.40 2.40 1.80 2.01 2.86 2.34 1.43 1.28Average annual rainfall 23.38 A7
  • Brownsville Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.07 0.34 0.01 0.00Maximum 4.79 10.25 5.72 10.35 9.12 8.52 9.43 9.56 20.18 17.12 7.69 3.98Median 0.77 0.84 0.41 0.84 1.86 2.22 0.96 2.45 4.69 2.92 0.90 0.78Average 1.31 1.38 0.80 1.62 2.39 2.55 1.50 2.69 5.19 3.62 1.55 1.10Average annual rainfall 25.70College Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.22 0.1 0.29 0.08 0.23 0.09 0 0 0.32 0 0.19 0.23Maximum 15.6 9.82 6.07 12.5 11.38 12.63 7.06 10.63 12.13 12.91 8.33 10.72Median 2.205 2.72 2.12 3.75 4.515 2.895 1.97 1.84 4.12 3.18 2.92 2.635Average 2.87 2.88 2.5 3.77 4.73 3.79 2.24 2.43 4.3 3.64 3.07 3.15Average annual rainfall 38.75Corpus Christi Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.01 0.00 0.00 0.00 0.00 0.03 0.00 0.10 0.49 0.00 0.00 0.01Maximum 10.78 8.11 4.89 8.04 9.38 13.35 11.92 14.79 20.33 11.88 5.24 9.80Median 0.99 1.36 0.78 1.39 2.70 2.43 1.04 2.64 4.00 2.60 1.34 0.90Average 1.54 1.85 1.36 2.03 3.12 3.16 1.80 3.28 5.21 3.50 1.57 1.59Average annual rainfall 30.00Dallas Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.00 0.25 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.18 0.13Maximum 8.46 7.60 8.70 15.40 13.74 10.30 7.34 5.12 10.67 14.00 7.54 8.90Median 1.80 2.11 2.36 2.98 4.27 2.85 1.60 1.74 2.50 2.94 2.00 2.10Average 1.97 2.40 2.91 3.81 5.01 3.12 2.04 2.07 2.67 3.76 2.70 2.64Average annual rainfall 35.10El Paso Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00Maximum 2.23 1.69 2.26 1.42 4.22 3.18 5.53 5.57 6.68 3.12 1.63 3.29Median 0.29 0.34 0.18 0.09 0.10 0.36 1.18 1.06 0.96 0.55 0.24 0.42Average 0.42 0.40 0.30 0.21 0.32 0.70 1.57 1.45 1.38 0.71 0.36 0.61Average annual rainfall 8.43 A8
  • Houston Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.36 0.38 0.11 0.43 0.04 0.26 0.45 0.31 0.80 0.05 0.41 0.64Maximum 9.78 5.99 8.52 10.92 14.39 16.28 8.10 9.42 11.35 16.05 10.07 9.34Median 2.82 2.63 3.19 2.59 5.02 3.55 2.69 3.52 3.92 3.79 3.27 3.41Average 3.68 2.95 3.40 3.54 5.36 5.07 3.05 3.69 4.31 4.63 4.09 3.54Average annual rainfall 48.45Lubbock Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Maximum 4.05 2.51 3.34 5.63 13.38 8.43 7.20 8.85 8.55 10.80 2.67 2.24Median 0.33 0.39 0.63 1.08 2.23 2.37 2.07 1.78 1.87 0.98 0.45 0.42Average 0.52 0.62 0.90 1.24 2.64 2.95 2.16 2.15 2.49 1.81 0.67 0.56Average annual rainfall 18.49San Angelo Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.00 0.01 0.00 0.00 0.26 0.05 0.00 0.00 0.00 0.00 0.00 0.00Maximum 3.65 4.47 5.00 5.10 11.24 6.01 7.21 8.13 11.00 8.68 3.55 3.98Median 0.58 0.62 0.65 1.29 2.32 2.09 0.70 1.38 2.38 1.90 0.68 0.33Average 0.79 1.04 0.92 1.66 2.78 2.20 1.10 1.75 2.83 2.24 0.98 0.76Average annual rainfall 19.12San Antonio Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.00 0.01 0.03 0.02 0.00 0.01 0.00 0.00 0.05 0.00 0.00 0.03Maximum 8.52 6.43 6.12 9.32 12.85 11.95 8.29 11.14 13.09 17.96 8.51 13.96Median 1.10 1.85 1.27 1.94 3.04 2.70 1.21 2.00 2.24 2.75 1.93 1.09Average 1.59 1.92 1.66 2.52 3.97 3.61 1.82 2.45 3.08 3.42 2.24 1.69Average annual rainfall 29.96Waco Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMinimum 0.03 0.00 0.04 0.12 0.52 0.27 0.00 0.00 0.00 0.00 0.13 0.04Maximum 5.92 7.69 5.56 13.37 15.00 12.06 8.58 8.91 7.29 10.51 7.03 9.72Median 1.55 2.00 2.22 2.76 3.87 2.34 0.82 0.96 2.57 2.37 2.29 1.94Average 1.83 2.28 2.25 3.30 4.49 2.98 1.82 1.76 3.02 3.12 2.40 2.31Average annual rainfall 31.68 A9
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  • Appendix C Case Studies Lady Bird Johnson Wildflower Center Austin4801 La Crosse AvenueAustin, Texas 78739(512) 292-4100http://www.wildflower.orgCapacity: 70,000 gallonsCatchment area: 17,000 square feetDemand: Gardens and landscapingHarvested rainwater from three separatecatchment areas provides 10 to 15 percent of thegarden and landscaping irrigation of the LadyBird Johnson National Wildflower ResearchCenter in Austin. An integral part of itsarchitecture, the Centers rainwater harvestingsystem serves to not only conserve water, butalso as a public education tool. The Centercollects water from 17,000 square feet of roofspace and can store more than 70,000 gallons inon-site cisterns.One of the most prominent features of the center The entry cistern at the Lady Bird Johnsonis the 43-foot native-stone-façade tower cistern, Wildflower Research Center is reminiscent ofwhich is built around a 5,000-gallon storage the stone-and-mortar cisterns used by Hilltank. Metal rooftops totaling an area of 17,000 Country settlers. Water from a 1,200-square-square feet drain into the tower cistern and two foot roof area is conveyed to the entry cistern25,000-gallon tanks collect a total of about via an aqueduct.300,000 gallons in an average rainfall year. Apressurized distribution system delivers water from the large tanks to an irrigationsystem. The municipal water supply is linked to the systems with backflow preventiondevices to prevent water contamination.The 3,000-gallon entry cistern, fed by an elevated stone-faced aqueduct draining just lessthan 1,200 square feet of roof area, is reminiscent of rainwater cisterns used by originalHill Country settlers. The Little House cistern captures rainwater from a roof area ofabout 700 square feet in the Children’s Area.In addition, the Wetland Pond, the Commons Well, and the Balcony Spring togethercollect 2,500 gallons per inch of rain from the roofs, although water from these features isnot used for irrigation. A11
  • H-E-B Austin6900 Brodie Lane(corner William Cannon Blvd. and Brodie Lane)Austin, Texas 78745Capacity: 28,000 gallonsCatchment area: 50,000 square feetDemand: Native and adapted plant landscapeTwo 8,000-gallon and two 6,000-gallon paintedsteel tanks are fed from a 24-inch-diametercollection pipe draining the 50,000-square-foot The H-E-B at the corner of Brodie Laneroof. Using efficient drip irrigation, captured and William Cannon Blvd. in south central Austin irrigates an adjacentrainwater irrigates an adjacent water-thrifty landscape of water-thrifty plants withlandscape of native and adapted trees and rainwater stored in four painted steelornamentals. Walkways and plant labels tanks totaling 28,000 gallons. A 24-inch-enhance the attractiveness of the site. diameter pipe conveys water from the roof to the tanks.The four tanks are connected with 6-inch PVCpipes and valves, allowing a tank to be takenoff-line to be drained and cleaned.H-E-B, based in San Antonio, prides itself onenvironmental stewardship in the communities where itssupermarkets conduct business. H-E-B saves 6.2 milliongallons of water annually by recycling condensation frommanufacturing steam equipment. Tanks are linked with 6- inch PVC pipe. Valves allow taking one or more tank off-line for draining or cleaning. A12
  • Sunset Canyon Pottery Dripping Springs4002 E. Highway 290Dripping Springs, Texas 78620(512) 894-0938Sunset Canyon Pottery supplies all its potable and pottery works water demand withwater stored in a 46,000-gallon ferrocement tank. When visiting this site on privateproperty, please first request permission from Sunset Canyon Pottery staff.The ferrocement tank at Sunset Canyon Pottery supplies process water for pottery works,as well as potable water for the straw-bale studio and gift shop. The tank was constructedfirst by forming an armature of steel reinforcement bars, then spraying on a cement-likematerial similar to that used for in-ground swimming pools. A13
  • New Braunfels Municipal Utility District New BraunfelsNew Braunfels Utilities Service Center355 FM 306New Braunfels, Texas 78130The New Braunfels Utilities Service Center,completed in 2004, captures rainwater in four1,000-gallon plastic-lined galvanized steeltanks, one located at each building wing.Water is used to irrigate the landscape ofnative and adapted plants. The metal tanksform both a practical and aesthetic feature ofthe architecture of this public building. Four lined, galvanized steel tanks will capture water for irrigation of native and adapted plants. A14
  • Hays County Cooperative Extension Office San Marcos1253 Civic Center LoopSan Marcos, Texas 78666(512) 393-2120Capacity: 750-gallon galvanized metal tank 1,600 polyethylene tankCatchment area: 2,500 square feetDemand: Demonstration gardenCost: $1,125The Hays County Extension Officecaptures rainwater from half the roofarea of its 5,000-square-foot building As a demonstration project, a 750-gallon galvanizedin two tanks: a 750-gallon galvanized steel tank captures rainwater from the 5,000-square- foot roof of the Hays County Extension Office.steel tank and a 1,600-gallon blackpolypropylene tank using existingguttering and downspouts. Plans are in the works for water to be gravity-fed to anadjacent Master Gardener demonstration garden. A15
  • Edwards Aquifer Authority San Antonio1615 N. St. Marys StreetSan Antonio, TX 78215(210) 222-2204Capacity: 2,500 gallonsCatchment area: 1,135 square feetDemand: LandscapingThe Edwards Aquifer Authoritycollects rainwater from a catchmentarea of 1,135 square feet in twocisterns. Water is delivered throughgravity flow into a 500-gallonpolypropylene tank in the courtyardarea. The second cistern, a 2,000- A 2,000-gallon, ranch-style metal cistern is one of two tanks that capture rainwater for landscaping at thegallon ranch-style metal cistern, is Edwards Aquifer Authority building. (Photo courtesy:located on the front lawn, visible from Lara Stuart)the street. Harvested rainwater is usedto irrigate the 266-square-footcourtyard, and 2,700-square-foot lawn. A16
  • J.M. Auld Lifetime Learning Center Kerrville1121 Second StreetKerrville, Texas 72028(830) 257-2218Capacity: 6,600 gallons (Two 3,300-gallon stacked concrete ring tanks)Catchment area: 5,000 square feetDemand: Adjacent gardens Pondless waterfallTotal Cost: $10,500Breakdown: Two 3,300 concrete tanks, $4,766 Plumbing supplies, $520 Pump, pressure tank, switch, $1,535 Gutter work, $541 Electrical supplies, $160 Trencher rental, $175 In-kind labor, Kerrville ISD, $2,800 Stacked concrete ring 3,000-gallon tank at the Auld Center, Kerrville,The Auld Lifelong Learning Center of Kerrville showing first flush diverter andIndependent School District is a community education cistern.facility operated by Kerrville Independent SchoolDistrict. Installed in 2003, two 3,300-gallon stacked concrete-ring tanks collect rainwaterfrom a 5,000-square-foot roof. Tanks are located at the back corners of the building, witha transverse 3-inch PVC pipe conveying the rainwater drained from the front half of theroof. Five-gallon first flush diverters at each corner capture the dust and debris of theinitial runoff of each rainfall event.Tanks are fitted with unique water-level sight gages. Vertical rods the same length as thetank height are suspended on floating platforms within the tank. The length of rodprotruding from the tops of tanks indicates water level.Captured rainwater will irrigate several adjacent themed gardens. In addition, a uniquewater feature, a recirculating waterfall, adds aesthetic interest. A17
  • Menard ISD Elementary School Menard200 Gay St.Menard, Texas 76859Container garden and landscape-plant irrigationCapacity: 1,000-gallon green polyethylene tankCatchment area: 600 square feetDemand: 50 emitters: 20 landscape plants, 30 container garden emittersTotal cost: $475Breakdown: Tank, $400 Connections and valves/roofwasher, $35 Using existing gutters and downspouts, Black poly pipe and emitters, rainwater harvesting techniques were used to $40 create a backyard wildscape. The principles of wildscape construction can be transferred toThe rainwater harvesting system serves large wildlife management programs.multiple purposes of education, beauty, andhabitat improvement at MenardIndependent School District ElementarySchool. The wildscape provides therequirements of food, water, and shelter fornative animals. The demonstration site aids inteaching students about healthful wildlifehabitats and container and landscapegardening. The water features, gazebo, androck walkway enhance the outdoor estheticsof the school. A backyard wildscape atMenard Elementary School demonstrates therequirements of food, water, and shelter forrangeland maintenance conducive tosupporting wildlife. Using existing gutters and Menard Elementary School rainwater harvesting installation showing downspout,downspouts from the roof of Menard 1,000-gallon poly tank, and gazebo (left)Elementary School, rainwater is diverted into surrounded by native and adapted landscapetwo 1,000-gallon green polypropylene tanks. plants. In this very attractive installation,One tank supplies a birdbath made of rocks harvested rainwater (using existing gutter andwith natural cavities and a prefabricated pond. downspouts) furnishes water not only to the landscape, but also to a watering pond,Both water features are supplied with water birdbath, and wildlife guzzler. (Photo courtesy:conveyed by gravity pressure through 3/4-inch Billy Kniffen)PVC pipe and drip emitters. Native plantsprovide a food source and cover for wildlife. A18
  • Walker County Cooperative Extension Office Huntsville102 Tam RoadHuntsville, Texas 77320(936) 435-2426Capacity: 550-gallon polyethylene tankCatchment area: 1,500 square feetDemand: Master Gardener demonstration plotTotal cost: Total: $230Breakdown: Used 550-gallon tank, $150 Plumbing supplies and fittings, $70 Glue, thinner, and paint, Rainwater captured from the 1,500-square-foot roof $10 of the Walker County Extension office is stored in a 550-gallon polypropylene tank, a type readilyThe Walker County Master Gardeners and available at ranch supply retailers. The 10-gallon flush diverter is the vertical standpipe visible to thestaff of Texas Cooperative Extension, left of the tank. Captured rainwater irrigates ansupervised by agricultural county agent adjacent Master Gardener demonstration garden,Reginald Lepley, installed a rainwater foreground.harvesting system at the Walker CountyExtension office for a cost of less than$250. A used white 550-gallon polypropylene tank was thoroughly cleaned and pressure-washed, and painted with brown latex paint to discourage algae growth. Raising the tankon concrete blocks allows gravity flow to a 10-foot by 25-foot Master Gardenerdemonstration garden. A detailed parts list, instructions and tips for rainwater harvestingin general, and more information on this installation can be found aturbantaex.tamu.edu/D9/Walker/AG/HomeHort/WCMG/hortdemo/Waterdemo/index A19
  • AMD/Spansion FAB25 Austin5204 E. Ben White Blvd.Austin, Texas 78741Rainwater drained from the facility’s roofs and groundwater from the building perimeterdrains furnish all the water needed for landscape irrigation on AMD’s Spansion site ineast Austin. Water is collected and stored in a 10,000-gallon fiberglass tank, and thenpressurized through the site irrigation loop using surplus pumps. The water savings hasbeen verified at about 4.75 million gallons per year using online flow meters. In-houseengineers designed the system and facilities tradespersons installed the tank, pump,piping, and electricity. The irrigation reclaim system has a three-year return oninvestment.The plant also has segregated drains that allow the reuse and recycling of rinse waterfrom the wafer manufacturing process for cooling tower and Ultra-pure treatment plantmakeup drastically reducing city-supplied water. The water savings from the rinse waterreuse system is approximately 210 million gallons per year and had a return oninvestment of less than one year. A20
  • J.J. Pickle Elementary School/St. John Community Center AustinCorner of Blessing and Wheatley AvenuesAustin, TexasA model of sustainable design andbuilding, the J.J. Pickle Elementary andSt. John Community Center in northeastAustin is a joint project of AustinIndependent School District and the Cityof Austin. Water from a portion of the116,200-square-foot facility drains intothree tanks, which provide cooling waterto the air-conditioning system.For energy savings, the classrooms, gym,dining area, and City library use sunlightrather than electric lights during the day.The complex opened in January 2002,with operational and maintenance costsavings of $100,000 expected each year.The complex includes a public elementaryschool, shared gymnasium, a healthcenter, public and school libraries, and acommunity policing office. The cost ofconstruction is $13.6 million, with theAISD funding about $8.3 million and the Water collected from the roof of the J.J. PickleCity of Austin funding about $5.3 million. Elementary School and St. John Community CenterThe money came from a 1996 School is stored in three large tanks behind the building andDistrict bond election and a City 1998 used as cooling water for the complex’s air- conditioning system.bond package. A21
  • Feather & Fur Animal Hospital Austin9125 Manchaca RoadAustin, Texas 78748Captured water from the roof,parking lot, and condensate fromthe air conditioners is the solesource irrigation water for a 1-acre turf landscape at the Feather& Fur Animal Hospital in SouthAustin. Dr. Howard Blatt firstexplored ways to make use of anexisting hand-dug 18,000-gallonunderground cistern. The projecthas since been expanded to takeadvantage of other rainwater The Feather & Fur Animal Hospital in South Austin features a standing-seam metal roof for rainwater harvesting.sources.Rainwater collected from astanding-seam metal roof gravity flows into the cistern. Then water from the parking lotflows through a water quality pond with gabion for sedimentation and filtrationtreatment. From the pond, water flows via a 6-inch pipe to catch basin. A small sumppump empties to a 12,500-gallon fiberglass tank. Additionally, the primary condensationline from the air handlers also drains into the gutter and downspout system, whichservices the roof. A22
  • Pomerening/Dunford Residence Bexar CountyThe Pomerening/Dunford family lives onthe western edge of Bexar County anduses rainwater harvesting for all of theirpotable needs. The four-year-oldinstallation features two 10,000-galloncisterns that store captured water from a2,400-square-foot collection area. Two 10,000-gallon cisterns collect rainwater at the Pomerening/Dunford residence in Bexar County. A23
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  • Appendix DTax Exemption Application Form A25