Rainwater collection is legal in California. Any residential, commercial, or governmental property owner can capture rain falling on their rooftop without a water rights permit from the state, and there is no state-imposed cap on how much you can store. What varies is the paperwork: a rain barrel for the garden needs almost nothing, while a system plumbed into your toilets or treated for drinking triggers building permits, health department review, and ongoing inspections.
The Law That Made It Legal
Assembly Bill 1750, signed in 2012, created the Rainwater Capture Act and placed it in the California Water Code starting at Section 10571. Its central provision is short and clear: capturing rainwater from your rooftop does not require a water right permit from the State Water Resources Control Board.1California Legislative Information. California Code, Water Code WAT 10574 Before the Act, California’s water rights system made it genuinely unclear whether catching rain in a barrel counted as diverting a water resource. The law settled that.
It authorizes rain barrel systems, outdoor non-potable capture systems, and indoor non-potable capture systems on developed or developing land.2California Legislative Information. California Assembly Bill 1750 – Rainwater Capture Act of 2012 It does not touch existing water rights, override local building authority, or reach rainwater use on agricultural lands.3California Legislative Information. California Code WAT Division 6 Part 2.4 10573 The California Building Standards Commission keeps its full authority to adopt building codes for these systems, and local agencies keep their permitting power for anything more complex than a barrel.
What Counts as Rainwater
The Water Code defines rainwater as precipitation falling on a public or private parcel that has not yet entered an offsite storm drain, flood control channel, or stream, and has not previously been put to beneficial use.3California Legislative Information. California Code WAT Division 6 Part 2.4 10573 Once water leaves your property and enters a storm drain or channel, it is no longer rainwater under this law, and different stormwater rules apply.
A rainwater capture system is a facility that captures, retains, and stores rainwater flowing off a building rooftop for later onsite use. A rain barrel system is a narrower category: it uses no electricity and no pump, and it has no connection to a potable water system.3California Legislative Information. California Code WAT Division 6 Part 2.4 10573 That definition matters because rain barrel systems get the lightest regulatory treatment.
What You Need Depends on What the Water Is For
The rules get stricter as you move from a garden barrel toward indoor plumbing or drinking water. Knowing which tier your project sits in prevents both over-engineering a simple setup and under-permitting a complex one.
Rain Barrels for Outdoor Use
A rain barrel used only for outdoor, non-potable purposes like watering a garden is the simplest case. The Rainwater Capture Act specifies that a landowner cannot be required to obtain a permit or authorization from a local agency as a condition of operating a rain barrel system that complies with the Act.4Legislative Counsel of California. AB 1750 Assembly Bill – Bill Analysis If your setup has no pump, no electricity, and no connection to your home’s plumbing, you can install it without filing anything. Systems storing less than 360 gallons for irrigation or car washing also have no minimum water quality requirements.5U.S. Environmental Protection Agency. Summary of California’s Water Reuse Guideline or Regulation for Rainwater Collected Onsite for Landscaping and Non-potable Water Reuse
Larger Outdoor Non-Potable Systems
A cistern with a pump feeding a drip irrigation network goes beyond the rain barrel exemption. Building permits may apply depending on your local jurisdiction, but the overall burden stays relatively light. Untreated rainwater used exclusively for surface, subsurface, or drip irrigation is regulated under Chapter 16 of the California Plumbing Code (Cal. Code Regs. tit. 24, § 5).5U.S. Environmental Protection Agency. Summary of California’s Water Reuse Guideline or Regulation for Rainwater Collected Onsite for Landscaping and Non-potable Water Reuse
Indoor Non-Potable Systems
Using captured rainwater indoors for flushing toilets or running a washing machine brings in more oversight. These systems must be permitted and inspected by the local agency, which is required to consult with the local public health department before issuing the first permit and may attach additional conditions. A second inspection under building standards enforcement is required before the system can be put into use.4Legislative Counsel of California. AB 1750 Assembly Bill – Bill Analysis Systems supplying toilets and urinals must include a debris excluder to keep leaves and other material out of the tank, together with a 100-micron filter.5U.S. Environmental Protection Agency. Summary of California’s Water Reuse Guideline or Regulation for Rainwater Collected Onsite for Landscaping and Non-potable Water Reuse
Where local rules do not exist, a default water quality standard applies: E. coli below 100 CFU per 100 mL and turbidity below 10 NTU. Local jurisdictions are not required to regulate onsite non-potable water systems, but many do.5U.S. Environmental Protection Agency. Summary of California’s Water Reuse Guideline or Regulation for Rainwater Collected Onsite for Landscaping and Non-potable Water Reuse
Potable Systems
Treating captured rainwater for drinking is the most heavily regulated option. A permit is required, and the system cannot have a direct connection to a public or private potable water supply or alternate water source. On initial startup, the local authority having jurisdiction, typically a plumbing, mechanical, or building official, determines whether the treated water meets quality standards for its intended use. Potable water filters must comply with NSF/ANSI Standard 53 and be installed according to the manufacturer’s instructions. If potable water from a public supply is used as makeup water for the storage tank, the connection must be protected by an air gap or backflow preventer. Ongoing inspections and maintenance follow the schedule in the California Plumbing Code (Table K 101.5.1) unless the manufacturer requires more frequent servicing, and owners must keep a maintenance log on-site and available for review.6U.S. Environmental Protection Agency. Summary of California’s Water Reuse Guideline or Regulation for Rainwater Collected Onsite for Potable Water Reuse
No State Cap on How Much You Can Collect
California puts no ceiling on how many gallons of rainwater you can capture. No maximum tank size is written into state law, and no volume alone triggers additional permitting. What scales up with size is the building and plumbing code side: a 55-gallon barrel under a downspout needs no permit, while a 5,000-gallon underground cistern with pumps and filtration will involve structural engineering, building permits, and plumbing inspections regardless of the end use.
Rainwater Is Not Graywater
California regulates the two separately, and mixing them up can send you to the wrong chapter of the code. Rainwater is precipitation collected from your rooftop before it reaches a storm drain. Graywater is wastewater from sinks, showers, bathtubs, and washing machines, but not toilets. Untreated graywater used for subsurface irrigation falls under Chapter 15 of the California Plumbing Code; untreated rainwater used for irrigation falls under Chapter 16.5U.S. Environmental Protection Agency. Summary of California’s Water Reuse Guideline or Regulation for Rainwater Collected Onsite for Landscaping and Non-potable Water Reuse Graywater generally faces stricter treatment requirements because it contains soap, food particles, and bacteria that rainwater does not.
Can an HOA Stop You
If you live in a community governed by a homeowners association, California law generally protects your ability to install water-efficient landscaping features under Civil Code Section 4750. The statute’s primary focus is drought-tolerant landscaping, and its protections extend broadly enough that an HOA would face difficulty prohibiting a properly installed rain barrel used for landscape irrigation. An HOA can still enforce reasonable aesthetic requirements, such as where a barrel sits or how it is screened from view. If yours pushes back, pointing to both the Rainwater Capture Act and Civil Code Section 4750 usually resolves the issue.
Rebates From Local Water Agencies
Several California water agencies offer rebates that offset the cost of equipment and installation. Programs vary by region and change periodically, so check with your local water provider before buying.
- San Francisco Public Utilities Commission pays up to $100 per rain barrel (maximum of two barrels) or up to $350 for one cistern with a capacity between 205 and 5,000 gallons.7San Francisco Public Utilities Commission. Rain Barrel and Cistern Rebate
- The Bay Area Water Supply and Conservation Agency (BAWSCA) pays up to $100 for barrels holding 50–99 gallons, up to $150 for 100–199 gallons, and up to $200 for 200 gallons or more, with participating member agencies in San Mateo County adding funds through June 2026.8BAWSCA. Rain Barrels
- Santa Clara Valley Water offers rebates for rain barrels, cisterns, and rain gardens for customers with existing gutter or downspout systems not currently capturing rainwater.9Santa Clara Valley Water. Rainwater Capture Rebate
Many other water districts across the state run similar programs. As of 2026, there is no statewide tax credit specifically for residential rainwater harvesting in California; the financial incentives are almost entirely rebate-based and funded by local water agencies.