The Texas Manual        onRainwater Harvesting Texas Water Development Board           Third Edition
The Texas Manual on Rainwater Harvesting         Texas Water Development Board                 in cooperation with        ...
AcknowledgmentsThe authors would like to thank the following persons for their assistance with theproduction of this guide...
Table of ContentsChapter 1 Introduction......................................................................................
Chapter 7 Financial and Other Incentives ................................................................... 53 Tax Exempt...
Chapter 1                                     IntroductionRainwater harvesting is an ancient                 extending the...
travels to the reservoir. While in                 of rainwater. The scope, method,residence in the reservoir, the water c...
growth areas, with large industrial            In fact, rainwater harvesting is  developments being plumbed for           ...
per day of condensate. An advantage of           Referencescondensate capture is that its maximum           Gould J, Nisse...
Chapter 2                   Rainwater Harvesting System ComponentsRainwater harvesting is the capture,             buildin...
the     surrounding          environment          harvested is usually suitable only for(Vasudevan, 2002).                ...
when considering a house plan with an              both before and after the storage tank.“L” or “T” configuration. A roof...
First-Flush Diverters                             A preliminary study by Rain WaterA roof can be a natural collection     ...
First-Flush Diverters                                        Standpipe                                        The simplest...
diversion devices will be required for            (handling rainwater from 1,500- andeach downspout.                      ...
For potable systems, storage tanks               truck, preferably near a driveway or  must never have been used to store ...
cylinder and low-horizontal cylinder              Polypropylene tanks do not retain paintconfigurations.                  ...
Metal                                             constructed of stacked rings with sealantGalvanized sheet metal tanks (F...
rainwater. For potable systems, it is                 Ferrocement structures (Figure 2-10)essential that the interior of t...
appropriate cistern type. Prior to making        rainwater installer is recommended toyour final selection, consulting wit...
Table 2-2. Cistern Types             MATERIAL                    FEATURES                          CAUTION    Plastics    ...
have to be more than 90 feet above thehouse.Since this elevation separation is rarelypractical or even desirable, two ways...
diverting 10 gallons for every 1,000square feet of roof is sufficient. If dripirrigation is planned, however, sedimentfilt...
filters in parallel installation, a UV light        water, referred to as “brine,” containingrated for a higher flow is ne...
Rain Water Harvesting and Waste Water           collected from rooftops in Bryan and  Systems Pty Ltd.,                   ...
Chapter 3                               Water Quality and TreatmentThe raindrop as it falls from the cloud is           ra...
maintaining disinfection equipment,            the state, acid rain is not considered a   such as cleaning and replacing  ...
Catchment surface                                the valve on the linking pipe betweenWhen rainwater comes in contact with...
Table 3-1. Treatment Techniques             METHOD                       LOCATION                           RESULT Treatme...
In either case, it is a good idea toChlorination                                      carefully dilute the chlorine source...
through sediment filtration before the              (See References.) The testing fee isultraviolet light treatment becaus...
www.dshs.state.tx.us/regions/default.         United States Environmental Protection  shtm                                ...
This page intentionally left blank.                28
Chapter 4                        Water Balance and System SizingThe basic rule for sizing any rainwater            suffici...
Figure 4-2. Average annual precipitationin Texas, in inchesFor planning purposes, therefore, these            volume of st...
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Texas water development board  the manual texas on rainwater harverting
Upcoming SlideShare
Loading in...5
×

Texas water development board the manual texas on rainwater harverting

10,626
-1

Published on

Published in: Education, Technology
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
10,626
On Slideshare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
57
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

Texas water development board the manual texas on rainwater harverting

  1. 1. The Texas Manual onRainwater Harvesting Texas Water Development Board Third Edition
  2. 2. 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
  3. 3. 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.
  4. 4. 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
  5. 5. 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
  6. 6. 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
  7. 7. 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
  8. 8. 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
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. 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
  13. 13. 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
  14. 14. 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
  15. 15. 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
  16. 16. 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
  17. 17. 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
  18. 18. 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
  19. 19. 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
  20. 20. 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
  21. 21. 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
  22. 22. 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
  23. 23. 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
  24. 24. 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
  25. 25. 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
  26. 26. 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
  27. 27. 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
  28. 28. 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
  29. 29. 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
  30. 30. 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
  31. 31. 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
  32. 32. 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
  33. 33. This page intentionally left blank. 28
  34. 34. 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
  35. 35. 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

×