Here is a summary of current graywater regulations from some western US states, with links to the sources for your further study.
Colorado Graywater Law
According to the Colorado Department of Public Health & Environment, in 2013 Colorado made gray water an opt-in program for local jurisdictions rather than a statewide program. Cities and counties may choose to recognize greywater but must adhere to the requirements in Regulation 86. They must also follow State Plumbing Board requirements regarding gray water piping in structures, and comply with state water rights laws.
In May 2024, the governor approved a bill to change the opt-in program to opt-out, meaning the default is now Yes, but it doesn’t go into effect until 2026, it only counts for new home construction, and it only covers indoor reuse, i.e. toilet flushing, not outdoor irrigation.
Colorado has long had deeply restrictive water laws. Only since 2016 has it been legal for homeowners to capture rainwater, and even now you’re limited to a paltry 110 gallons.
Among other things, Regulation 86 requires design flow calculations. This means you’ll need to know how many gallons of water go through your washer each week, as well as how much water runs through your showers and sinks if you plan to hook those up too. Limitations are specified on daily flow. Click the links, read the fine print, and check with both your city and county.
Arizona Graywater Law
Arizona loosened up tight restrictions in 1998, and now the Arizona Department of Environmental Quality encourages gray water use without requiring a permit, as long as it’s less than 400 gallons a day. You’ll also need to be sure that the water table is at least 5 feet below the surface. Read their Best Management Practices here. You can also download the relevant chapter of the Arizona Administrative Code from that page.
The guidelines are rather light on explanation in terms of chemistry: “It’s important to understand which chemicals go down household drains, as you don’t want to use gray water with elevated levels of chlorides, sodium, borax or sulfate that has a high pH, which could be harmful to your plants.” That’s all you get. This is pretty surprising given how arid the environment is there. Make sure to review the advice on our Soaps page.
Washington State Graywater Laws
The Washington State Department of Health adopted new greywater laws in 2011. They specify that you can only release greywater during the growing season and only in suitable soil, both of which are defined in the code.
Washington also splits greywater usage into three Tiers, defining Tier 1 as a light greywater irrigation system with maximum design flows of 60 gallons a day serving a single-family residence. Tier 2 allows for residential or non-residential buildings, and Tier 3 actually allows the inclusion of “dark” greywater, including flows from dishwashers and from kitchen and non-laundry utility sinks, provided there is a “treatment component” involved.
A number of details are left to local jurisdictions, so you’ll still need to check in with your local authorities
Oregon Graywater Laws
Oregon also recognizes three Tiers of greywater, but they organize things a bit differently from Washington. For one thing, they include kitchen sink water in Tier 1. But they also require that you include a physical process to remove solids, including from your laundry.
They require a permit for every Tier, the permit has to be renewed regularly, and you have to submit an annual report certifying operational compliance.
The Department of Environmental Quality has the details.
Nevada Graywater Laws
Nevada allows greywater use, mostly according to the standard best practices on our Legal page. However, it’s limited to single family dwellings. As Nevada’s water woes continue to worsen, legislators may yet see the light and update the code to include duplexes and apartment buildings.
You are required to have a permit in all cases, not making an exception for laundry to landscape. Oddly, the code also requires a surge tank, even though it also says you could rely on gravity if you’d rather not include a pump.
Unlike some state codes, Nevada’s is easy to read. Find the text of NAC 444.837 here.
You’ll need to check your soil percolation rate, as the upper limit is 120 minutes per inch. The code gives detailed instructions for how to do this, lower down the page at NAC 444.796. This is a great bonus, and a useful tool for anyone in any state.
California Graywater Laws
California classes outflow from kitchen sinks and dishwashers as black water.
The way California handles the 3-Tier idea is with three categories: Clothes Washer Systems, Simple Systems (up to 250 gallons a day) and Complex Systems (over 250 gallons a day).
The California Department of General Services has a link to the 2022 California Plumbing Code, but the link is unnecessarily hard to find on the page. It takes you to the IAPMO site for reading, where the relevant section is Chapter 15, Alternate Water Sources for Nonpotable Applications.
It’s pretty dense (and the interactive display tool can be quite irritating), but once you understand the pattern we’ve been laying out on this site, you’ll see it clearly enough through the legalese.
The Clothes Washer System part starts at section 1503.1. It does say that although you don’t need a permit for laundry to landscape, you do have to know whether your local authority requires you to notify them of what you’re doing. It also says cities and counties may be more restrictive if they choose to be, so that’s another reason to look up who’s in charge of water regulations in your vicinity.
And the code says a surge tank is only necessary when the distribution system can’t absorb all the peak flow at once – the point is that greywater must not be allowed to pool or run off on the surface where it can come into contact with people or animals. If your mulch basins aren’t large enough to contain max flow, the best thing would be to make them larger. Second best would be to include a surge tank and a pump so the extra doesn’t get out and make a problem.