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Texas Manual on Rainwater Harvesting

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Texas Manual on Rainwater Harvesting The Texas Manual on Rainwater Harvesting Texas Water Development Board Third Edition The Texas Manual on Rainwater Harvesting Texas Water Development Board in cooperation with Chris Brown Consulting Jan Gerston Consulting Stephen Colley/Architecture Dr. Hari J. Krishna, P.E., Contract Manager Third Edition 2005 Austin, Texas Acknowledgments The authors would like to thank the following persons for their assistance with the production of this guide: Dr. Hari Krishna, Contract Manager, Texas Water Development Board, and President, American Rainwater Catchment Systems Association (ARCSA); Jen and Paul Radlet, Save the Rain; Richard Heinichen, Tank Town; John Kight, Kendall County Commissioner and Save the Rain board member; Katherine Crawford, Golden Eagle Landscapes; Carolyn Hall, Timbertanks; Dr. Howard Blatt, Feather & Fur Animal Hospital; Dan Wilcox, Advanced Micro Devices; Ron Kreykes, ARCSA board member; Dan Pomerening and Mary Dunford, Bexar County; Billy Kniffen, Menard County Cooperative Extension; Javier Hernandez, Edwards Aquifer Authority; Lara Stuart, CBC; Wendi Kimura, CBC. We also acknowledge the authors of the previous edition of this publication, The Texas Guide to Rainwater Harvesting, Gail Vittori and Wendy Price Todd, AIA. Disclaimer The use of brand names in this publication does not indicate an endorsement by the Texas Water 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 views of the Texas Water Development Board, or any other entity. Table of Contents Chapter 1 Introduction..................................................................................................... 1 Chapter 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........................................................................ 17 Chapter 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 ........................................................................................................... 23 Chapter 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 ............................................................................ 36 Chapter 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...................................................................... 43 Chapter 6 Cost Estimation............................................................................................. 45 Comparing to Other Sources of Water.......................................................................... 51 i Chapter 7 Financial and Other Incentives ................................................................... 53 Tax Exemptions ............................................................................................................ 53 Municipal Incentives..................................................................................................... 54 Rainwater Harvesting at State Facilities....................................................................... 55 Performance Contracting .............................................................................................. 56 Appendix A References ................................................................................................. A1 Appendix B Rainfall Data ............................................................................................. A7 Appendix C Case Studies ............................................................................................ A11 Appendix D Tax Exemption Application Form ........................................................ A25 ii Chapter 1 Introduction Rainwater harvesting is an ancient extending their use; rainwater technique enjoying a revival in eliminates the need for a water popularity due to the inherent quality of softener and the salts added during rainwater and interest in reducing the softening process. consumption of treated water. Rainwater is sodium-free, important Rainwater is valued for its purity and for persons on low-sodium diets. softness. It has a nearly neutral pH, and Rainwater is superior for landscape is free from disinfection by-products, irrigation. salts, minerals, and other natural and man-made contaminants. Plants thrive Rainwater harvesting reduces flow to under irrigation with stored rainwater. stormwater drains and also reduces Appliances last longer when free from non-point source pollution. the corrosive or scale effects of hard Rainwater harvesting helps utilities water. Users with potable systems prefer reduce the summer demand peak and the superior taste and cleansing delay expansion of existing water properties of rainwater. treatment plants. Archeological evidence attests to the Rainwater harvesting reduces capture of rainwater as far back as 4,000 consumers’ utility bills. years ago, and the concept of rainwater Perhaps one of the most interesting harvesting in China may date back 6,000 aspects of rainwater harvesting is years. 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 resource hillsides for agricultural and domestic at the place it occurs. This natural purposes are still standing in Israel synergy excludes at least a portion of (Gould and Nissen-Petersen, 1999). water use from the water distribution Advantages and benefits of rainwater infrastructure: the centralized treatment harvesting 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 features to channel and concentrate The end use of harvested water is located close to the source, rainwater in either storage basins or eliminating the need for complex and planted areas. costly distribution systems. When assessing the health risks of Rainwater provides a water source drinking rainwater, consider the path when groundwater is unacceptable or taken by the raindrop through a unavailable, or it can augment limited watershed into a reservoir, through groundwater supplies. public drinking water treatment and distribution systems to the end user. The zero hardness of rainwater helps Being the universal solvent, water prevent scale on appliances, absorbs contaminants and minerals on its 1 travels to the reservoir. While in of rainwater. The scope, method, residence in the reservoir, the water
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