Rainwater Harvesting and Water Conservation
Summary
Rainwater harvesting collects roof runoff in a cistern for irrigation and other nonpotable uses. Size the cistern against supply and demand over time and keep first flows out of storage, since treatment and permitting depend on the intended use.
Cols
Scope
- Typical nonpotable uses: irrigation, toilet flushing, vehicle washing, clothes washing
- Potable use: a treatment system for indoor potable use typically requires health department approval
Components
- Catchment and conveyance: roof, gutters, and leaders
- Pre-storage treatment: divert debris and first flows before storage; a roof washer traps the first flow and routes it away from the cistern
- Storage: cistern sized to the budget below
- Distribution: pump and piping to the point of use
Selection
- Water budget model: run a simple supply and demand model for several cistern sizes and compare the output; this is the preferred sizing method in one state design manual
- Curve method: one stormwater program sizes cisterns from curves of drawdown time and volume for toilet-flushing demand, assuming 1 acre of tributary impervious area
- Local rules: collection, treatment, and cross-connection requirements are set by the jurisdiction
Sources
- North Carolina Department of Agriculture: cistern design manual, https://ncagr.gov/soil-water/swcccap-cistern-design-manual/open
- Santa Clara Valley Urban Runoff Pollution Prevention Program: Appendix I, https://scvurppp.org/wp-content/uploads/2024/07/Appendix-I-2024.pdf
- University of Florida IFAS: cisterns for nonpotable use, https://www.ctahr.hawaii.edu/hawaiirain/Library/Guides&Manuals/FL_Cisterns_NonPotable_Use.pdf
- Wikimedia Commons: 20140530-AMS-LSC-9001 - Peoples Garden - Rain Barrel (15498316125).jpg, by U.S. Department of Agriculture (Public domain), https://commons.wikimedia.org/wiki/File:20140530-AMS-LSC-9001_-_Peoples_Garden_-_Rain_Barrel_(15498316125).jpg