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Whole House Rainwater Harvesting: Capturing and Using Rainwater for Potable Applications


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For a number of reasons, rainwater harvesting is preferred not just for landscape irrigation but for whole house potable uses as well. Here we present advanced design concerns and strategies …

For a number of reasons, rainwater harvesting is preferred not just for landscape irrigation but for whole house potable uses as well. Here we present advanced design concerns and strategies including reliability, safety, regulatory and legal issues.

Presented to the Conservation Coordination Consortium hosted at Tampa Bay Water, October 13, 2010

Published in: Technology

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  • RHS= Rainwater Harvesting System
  • LID = Low Impact DevelopmentSite retention = reduced demand on stormwater processingA good strategy would be to, not only conserve water, but also to use an alternative water source (rainwater) for irrigation, and save our precious potable drinking water for drinking and other indoor uses.Not as cost-effective for small volumes, but for large = huge potential financial savings
  • Simple supply and demandRapidly and continuously growing region = resource demandsIncreased demand on traditional water supplies (ground/surface water) = growing reliance on “innovative” supplies (desal)Groundwater demand leads to unstable geology (sinkholes)??Increased pollution = increased treatment efforts (surface waters)As demand on “innovative” supplies increase, cost of blended product increasesRHS is an alternative supply that reduces demand on produced water resources
  • How do we prolong development of new water supplies?As a part of effective conservation: RAINWATER HARVESTING
  • There are many uses for rainwater. Irrigation would be the application requiring the least amount of treatment before use.All contribute to offsetting municipal supplies.
  • HEALTH is #1 priority. (repeated for emphasis).Treatment to potable standardsTesting to ensure standards are metReliable (don’t want loss of water during shower)Ease of serviceRegulatory = building, health, etcProbably incomplete list
  • As it pertains to water qualityBig or small, residential or commercial, the harvesting system will have these components.Focus on: 1) pre-treatment; 2) Treatment; 3) reliability
  • The roof is what is used as the catchment area. (there are other surfaces, e.g. permeable driveways, swales, etc… but for simplicity, stick with roofs)Its size dictates how much rainwater can be captured. Material affects initial water quality.The slicker, the better
  • Common senseGarbage in, garbage out
  • First line of defense.Not reliable. When designing RHS, assume no leaf guards.Keeping limbs and leaves away from catchment area and from clogging conveyance is important in keeping cistern water quality pure.These products reduce maintenance needs while preventing debris from entering the cistern.
  • First-flush or roof washerVolume to be diverted depends on contaminant loadMinimal (no large overhanging trees)= ~ 10 gallons/1000 sfHeavy (large overhanging tree canopy) = ~ 50+ gallons/1000 sf
  • You will notice that cisterns have a lot pipes going in and out of them. This configuration can vary, but generally there will be an inlet, an outlet, an overflow and drain valve. A manway is also necessary for maintenance/cleaning. Never go inside alone or without a plan on how to get out.Inlet, outlet and overflow are self explanatory. Overflow:Engineering drainage design may need to come into play here. Common sense dictates for overflow to be directed away from tank/buildings where volume of water won’t cause erosion, flooding, carry organic material (especially if animals are present) into wells or water sources, cause standing water for long periods (mosquito breeding), etc. Over flow can be directed towards in place drainage system or can also be allowed to percolate into the ground via french drain, etc. Passive use of the overflow rainwater is desirable.Overflow outlets can be configured in different ways. If the overflow outlet draws from the bottom, it should be vented to prevent siphoning. Overflow outlets and vents should be equipped with a fine mesh screen to prevent mosquito entry.Anaerobic/Sediment zone is located in the bottom 6” or so of the tank. Here is where the ‘dirtier’ water and sediment tends to collect. Avoid drawing water from this portion of the tank.A hose bibb or drain valve is needed in order to drain the tank if needed. Bibb should be elevated 6” or so. Solids tend to accumulate at the bottom so elevating will help avoid clogging.The floating suction filter will allow water to be extracted in the cleaner area of the tank. Particles either settle at the bottom of the tank or float on top. Thus, the filter on the end of the hose will filter the remainder of the particles before sending the water to the irrigation system.Important to make sure all openings are sealed properly to avoid (1) mosquito infestation (2) animal intrusion and (3) children from entering the cistern.Tank should be placed on a level, stable foundation. This may consist of gravel or concrete pad. FACT: Water weighs 8.34 pounds per gallon. A 1000 gallon cistern can weigh up to 8340 gallons when full. Imagine what would happen if an unstable tank tips over.
  • Pump:Make-up: valve to switch to other water source when tanks run dry or water quality is low-In this case, normally open = fail-safe redundancy
  • Dual pump for increased demandNo less than 3 backflow preventers in this roomSwitching controls for make-up water
  • NOTE 1: Dye injection for toilet flushing, per greywater plumbing codes. If treated for potable, must meet EPA standards, approval from health, water resources departmentsNOTE 2: Backflow to prevent public water supply (if cross-connected to municipal water)UV preferred for small-scale RHS because non-chemical (e.g. chlorine) and doesn’t waste water (e.g. RO)NSF 53: Guideline for removal of cysts: 0.5 um carbon.NSF 55A: Guideline for ultraviolet treatment of previously untreated surface waters. Must be pre-treated to NSF 53.All RWS potable systems use components that meet NSF 53 and 55A (also 61: components safe for drinking water)
  • Typical potable treatment: 2 (or more) stage sediment/carbon + UV disinfection
  • Pump2-stage sediment/carbonUVNote: backflow prevention
  • Pump3-stage sediment/carbonUVNote: makeup controlsFloat switch and UVT switch wired in series to NO valve on mains water
  • Complex systems require collaboration and knowledge of various regulations, laws and guidelines
  • Engineer is your best friendMUST HAVE QUALITY ENGINEERINGIncludes meetings with building department officials as needed. Keep everyone in the loop.
  • Commonly, rainwater is considered as “graywater” for lack of a better definition. However, according to IPC 2006 (Appendix C: C101.9), Gray Water is defined asGray Water: “waste discharged from lavatories, bathtubs, showers, clothes washers, and laundry trays.”IPC 2006; Appendix C: C101.9Since water collected in RHS is not supplied by any of the sources listed in this definition, an argument can reasonably be presented that rainwater is NOT graywater. As such, RHS should not be subject to the same code interpretations as graywater.Since surface waters (including stored rainwater) are suitable as private water supplies, the only limitations on their use for the proposed applications pertain to their potability.Potable Water: “Water free from impurities present in amounts sufficient to cause disease or harmful physiological effects and conforming to the bacteriological and chemical quality requirements of the Public Health Service Drinking Water Standards or the regulations of the public health authority having jurisdiction.”Florida Building Code 2007: Plumbing Code; Section 202Stormwater often the most overlooked part of RHSInexperienced designers don’t consider the cumulative flow rate (if 3 x 4” pipes going in, better have at least 6” pipe going out).Example: builder responsible for storm drainage. RWS left 6” pipe stubbed out from tanks for overflow of catchment off a 4000 sf roof. Builder connected with 3” pipe. Led to “geyser” and flood of neighbor’s low-lying pool. Pool damaged, popped out of ground, etc…
  • “Surface Water: Surface water accumulates mainly as a result of direct runoff from precipitation. Precipitation that does not seep into the ground or evaporate, flows over the ground surface and is classified as direct runoff…In some areas, a source of water is the rainfall intercepted by roof surfaces on homes, barns, and other buildings. Water from those surfaces can be collected and stored in tanks called cisterns.”Manual for Individual and Non-community Water Supply SystemsUnited States EPA, Office of WaterDocument: EPA 570/9-91-004In order for regulatory agencies to evaluate potability of water supplies, the EPA provides updated standards for drinking water contaminants (see: Treatment methods must meet or exceed the values specified by these standards.
  • Also cost will become more relevant as existing resources are depletedBackflow, testing, make-up supply, communicationEngineer is best friendNSF 53, NSF 55A, etcMake-up water controls. Not only level switched, also water quality switched.All involved from the beginning. All on same page throughout process.Still a lot of questions and misunderstanding. Need more education of all involved: - property owners - builders - engineers/architects (designers) - building officials - etc
  • Contact info, social networking feedsPresentation available to public on slideshare
  • Transcript

    • 1. Whole House Rainwater Harvesting:
      Capturing and Using Rainwater for Potable Applications
      Brian Gregson
      Rainwater Catchment Systems Accredited Professional
      Photo credit:
      REAL Building Group LLC
      Conservation Coordination Consortium
      Tampa Bay Water
      October 13, 2010
    • 2. Who we are
      Irrigation Contractor
      Specializing in highly efficient water-conservation solutions
      Drip/micro irrigation, landscape drainage
      ARCSA AP in State of FL
      Permitted RHS in St. Pete
      Institutional rainwater toilet flushing in St. Pete
      Potable RHS in St. Pete
      Potable RHS in Tampa
      Permitted greywater(??) in Tampa
      Shifting focus to commercial applications
    • 3. Why harvest rainwater?
      Preserve potable water for drinking and indoor uses
      Stormwater management
      Contribute to responsible growth
      Larger volume = $$$$
    • 4. The PROBLEM:
      Population growth = greater demand on resources (power, water, etc)
      Reduced reliance on groundwater/surface water
      Greater reliance on “innovative” water supplies (e.g. desalination)
      RHS reduces demand on blended resources
    • 5. Rainwater Harvesting:A Sustainable Option
    • 6. Possible Uses for Rainwater
      Other Outdoor
      Vehicle washing
      Swimming pool makeup
      Industrial processes instead of municipally treated water
      Cooling tower makeup
      Toilet flushing
      Ease watering restrictions when RHS used for the above??
    • 7. General Considerations:POTABLE APPLICATIONS
      Alternate source (if available?)
      Replaceable/serviceable components
    • 8. System Anatomy
      The ON button!
      Catchment Area
      (screen filters, first-flush)
      Treatment & Distribution
      Source: Harvesting Water for Landscape Use by Patricia H. Waterfall, p. 34 Original diagram was modified for this application.
    • 9. Catchment
      Roof acts as the catchment area
      Determines harvesting potential
      Surface material
      Determines quality
      The slicker, the better
      For potable, metal is preferred
      Courtesy: ARCSA
    • 10. Conveyance & Pretreatment
      Water quality is determined by what is conveyed into the storage tank(s)
      Roof surface debris
      Twigs and leaves
      Bird droppings
      Other debris
    • 11. Conveyance & Pre-treatment
      Leaf Guards
      First line of defense
      Screened rain heads
      Finer, pre-tank protection
    • 12. First Flush Devices
      Prevents initial volume (“first-flush”) of roof runoff from entering storage tanks.
      After a rainfall event, the “dirty” water is released through a slow-release valve, to reset for the next rainfall.
      10-50 gallons per 1000 sf roof area
    • 13. First Flush Devices
      Downspout (wall-mounted)
    • 14. Cistern Anatomy
      Lid or manway
      Secured tightly to avoid entrance by children and animals.
      Use fine mesh screen to keep mosquitoes out
      Max Water Level
      Use flap valve or other methods to keep insects and animals out
      From downspouts
      Turbulence calming device (optional)
      To prevent remixing of sediment
      Floating Suction Filter
      Tank Pad
      To distribution
      Source: Rainwater Harvesting Planning and Installation Manual, January 2009, Figure 12.5. Original diagram was modified for this application.
      Anaerobic / Sediment
      Hose Bibb
    • 15. Distribution
      Select appropriate pump/pressure tank for water demand
      Connect to disinfected indoor supply and/or irrigation system
      Makeup water supply (if available) for low-water and/or poor water quality conditions
      Backflow prevention!!!
      Backflow prevention!!!
    • 16. Major Distribution Components:RELIABILITY
    • Distribution:EXAMPLE
    • 19. Treatment
      Treatment processes
      2 or more stage + carbon
      NSF 53 = cyst removal
      NSF 55A = UV treatment of surface water
      Other disinfection options:
      Chlorine, Ozone, RO, etc…
      All Rainwater Services potable systems meet NSF 53 and 55A
    • 20. Treatment
    • 21. Disinfection & Treatment:EXAMPLE
    • 22. Disinfection & Treatment:EXAMPLE
    • 23. Regulatory Consideration
      Engineering, engineering, engineering
      Building codes
      Graywater(for non-potable)
      Health Departments
      EPA: Guidelines for surface water treatment
    • 24. Regulatory Considerations:ENGINEERING
      Makeup water controls
      Backflow prevention
      Stormwater drainage
      Makeup water controls
      Distribution/treatment components
      RHS is relatively new/misunderstood. Few guidelines/codes/laws exist. Those that do aren’t necessarily clear. To ensure all building codes and building department concerns are met,
    • 25. Regulatory Considerations:BUILDING CODES
      Classification of rainwater leads to confusion
      IPC does not directly address rainwater, which leads to confusion and misunderstanding
      Too often, rainwater is considered as “graywater” for lack of a better definition
      Graywater = “waste discharged from lavatories, bathtubs, showers, clothes washers, and laundry trays.” (IPC 2006; Appendix C: C101.9)
      Rainwater is not graywater!!
      Rainwater IS surface water
      Surface water is suitable water supply (Florida Building Code 2007: Plumbing Code; Section 202)
      Stormwater drainage
      Too often overlooked/afterthought
      Vertical and horizontal leaders must be sized appropriately (FBC 2007: Plumbing Code; Section 1106)
      Tampa Bay 100 year rainfall event = 5”
      What flows into tanks must flow out at same rate
      All downspouts lead to a common point. Total flow rate is cumulative.
      When in doubt, scale up the overflow
    • 26. Regulatory Considerations:HEALTH DEPARTMENTS
      Surface water private water supplies
      For private water supplies, no state code requiring water quality sampling exists
      However, recommended to test with same frequency as public well and/or surface water systems
      Rainwater Services tests new potable systems for bacteria, lead and nitrates upon installation and as needed thereafter
    • 27. Regulatory Consideration:EPA
      Defines surface water
      Rainwater harvested in cisterns falls under the surface water definition
      Manual for Individual and Non-community Water Supply Systems
      United States EPA, Office of Water
      Provides standards for drinking water contaminants
    • 28. Summary
      Harvested rainwater is a viable and practical water supply
      For potable applications, strict attention must be paid to health, reliability & regulatory concerns
      An effective system begins with proper design
      Finished product must meet recognized standards for potability
      Fail-safe reliability (redundancy) must be considered
      Design and construction is a collaborative effort involving various trades, engineers and building officials
      Education is key to widespread adoption of rainwater harvesting codes, regulation and guidelines
    • 29. Many thanks…
    • 30. Questions?
      Brian Gregson