Collecting rainwater in California is legal statewide. The Rainwater Capture Act of 2012 gives residential, commercial, and government property owners the right to install a system that captures rain from their rooftops and stores it for use on the same property.1California Legislative Information. California Water Code WAT Section 10573 What you can do with that water, and whether you need a permit to install the equipment, depends on system size, where the water goes, and your local building and health rules.
What the Rainwater Capture Act Allows
Assembly Bill 1750, the Rainwater Capture Act of 2012, passed both chambers of the state legislature unanimously.2Ballotpedia. California Proposition 72, Rainwater Capture Systems Excluded from Property Tax Assessments Amendment (June 2018) It defines a rainwater capture system as a facility designed to capture, retain, and store rainwater flowing off a building rooftop for later onsite use. Two words in that definition do most of the work: rooftop and onsite. You can collect what falls on your roof, and you can use it on the property where you collected it. Diverting water from a creek or channeling runoff across property lines is a different question governed by California’s water rights system, not by this law.
What You Can Use Collected Rainwater For
Most collected rainwater is put to non-potable use. Under California’s plumbing code, approved applications include landscape irrigation (surface, subsurface, drip, and spray), toilet and urinal flushing, clothes washing, car washing, ornamental fountains, and cooling tower makeup water.3US EPA. Summary of California’s Water Reuse Guideline or Regulation for Rainwater Collected Onsite for Landscaping and Non-potable Water Reuse Outdoor irrigation is the most common use and where the water bill savings show up.
Piping rainwater into your house for toilet flushing adds requirements. The California Plumbing Code requires a debris excluder on the storage tank and a 100-micron filter on water supplied to toilets and urinals. The water itself must show an E. coli count below 100 CFU per 100 mL and turbidity under 10 NTU.3US EPA. Summary of California’s Water Reuse Guideline or Regulation for Rainwater Collected Onsite for Landscaping and Non-potable Water Reuse
Drinking Collected Rainwater
California allows potable use of harvested rainwater, but the bar is high. A system intended for drinking, cooking, or bathing must meet the maximum contaminant levels in Title 22 of the California Code of Regulations.4State Water Resources Control Board. Contaminants in Drinking Water The CDC warns that rainwater is not safe to drink until germs and chemicals have been removed, and recommends regular testing when it is used for drinking, cooking, or bathing.5Centers for Disease Control and Prevention. Collecting Rainwater and Your Health: An Overview For most homeowners, the cost of treatment and monitoring outweighs the benefit, and non-potable uses are where the practical payoff sits.
Permits and Local Rules
State law establishes the right to collect; your city or county controls how the system gets installed. Whether you need a building permit depends mostly on tank size. In many California jurisdictions, water tanks that sit on the ground and hold 5,000 gallons or less are exempt from building permits, provided the tank’s height-to-diameter ratio stays within limits. Tanks above 5,000 gallons typically require a building permit and an engineer-designed foundation with seismic support.6San Francisco Public Utilities Commission. Rain Barrel and Cistern Rebate A simple rain barrel hooked to a downspout usually needs nothing. Any system that ties into your home’s plumbing will almost certainly need a plumbing permit regardless of tank size. Call your local building department before you start.
Local health and vector control rules add another layer. Rain barrels and cisterns need to be sealed or screened tightly enough that mosquitoes cannot get to standing water, and vector control agencies can cite properties where storage is left open. Inspect seals and screens at the beginning and end of each rainy season.
Connecting to Household Plumbing
If your system feeds indoor fixtures, the California Plumbing Code requires strict separation between rainwater and the municipal supply. A potable rainwater catchment system cannot have a direct connection to a public or private potable water supply. Where municipal water backs up an empty tank, the connection must be protected by an air gap or a backflow preventer to keep untreated rainwater from flowing into the municipal system. Components must also be inspected and maintained on the schedule set by the California Plumbing Code, unless the manufacturer calls for something more frequent.7US EPA. Summary of California’s Water Reuse Guideline or Regulation for Rainwater Collected Onsite for Potable Water Reuse A plumber familiar with rainwater systems is worth the call.
Property Tax Exclusion
Home improvements normally raise your property’s assessed value. Rainwater capture is an exception. California voters approved Proposition 72 in 2018, and the Legislature implemented it by excluding the value of any rainwater capture system installed between January 1, 2019 and December 31, 2028 from a property’s taxable value. The exclusion stays in place until the property changes hands.8Legislative Analyst’s Office. Proposition 72 For most residential systems the tax savings are modest, but larger cisterns and commercial installations make the exclusion worth claiming. Notify your county assessor after installation.
Rebate Programs
Many California water agencies offset the cost of equipment through rebates, and the amounts vary by district. The San Francisco Public Utilities Commission offers up to $100 per rain barrel (maximum of two) and up to $350 for a cistern between 205 and 5,000 gallons.6San Francisco Public Utilities Commission. Rain Barrel and Cistern Rebate In San Diego County, the SoCal WaterSmart program pays up to $35 per rain barrel (up to two per home) and $250 to $350 for cisterns depending on capacity.9San Diego County Water Authority. Residential Rebates and Programs Santa Clara Valley Water District offers rebates for rain barrels, cisterns, and rain gardens.10Santa Clara Valley Water District. Rainwater Capture Rebate
Funding levels shift year to year. Some programs require pre-approval before purchase, and most ask for receipts and photos of the finished installation. Check your local water utility’s current program before you buy.
What You Can Realistically Collect
A rough formula sets expectations: every inch of rain on 1,000 square feet of roof yields about 600 gallons. A 1,500-square-foot roof in a part of California that receives 15 inches a year could theoretically collect around 13,500 gallons. Real-world numbers come in lower after evaporation, first-flush diversion, and gutter losses, but even a conservative figure runs well above what a 50- or 100-gallon rain barrel can hold.
The mismatch matters when you’re sizing a system. A single barrel fills fast in a moderate storm, and once it’s full the overflow heads to the storm drain. If the goal is a meaningful cut in your water bill, a cistern in the 500- to 2,500-gallon range holds enough to irrigate through dry stretches between storms. Basic rain barrel setups run a few hundred dollars; a professionally installed cistern usually runs a few thousand. Payback comes fastest in areas with tiered water pricing, where reducing outdoor use can drop you into a cheaper rate bracket.