Laundry-to-Landscape Graywater and Rooftop Rain: The Basic Rules

On a dry north county lot, the rinse water from a washing machine can go to fruit trees instead of the septic tank or sewer. Paso Robles averages 15.26 inches of rain a year at the in-town station, per NOAA's 1991-2020 normals, and almost none of it falls in summer, so reused water has obvious appeal.

When does a washer graywater line need no permit?

When it runs from a clothes washer in a one- or two-family home, does not alter the household plumbing, and meets the California Plumbing Code's listed conditions. A UC Agriculture and Natural Resources publication quoting Chapter 15 of the code lists them. In short: notify the local agency if it asks for notice; fit a labeled valve that sends flow to the yard or to the sewer; use no potable water connection and no pump other than the washer's own; keep the water on the site; allow no ponding or runoff; cover each outlet with at least 2 inches of mulch, rock or soil, or a solid shield; send diaper water to the sewer; leave out hazardous chemicals; and keep an operation manual with the house.

That list reflects an older code edition. A new state plumbing code took effect January 1, 2026, so confirm today's wording with SLO County Planning & Building before digging.

Anything more ambitious changes the picture. According to the county's UC Master Gardeners, altering the house plumbing, drawing from a shower, bath or bathroom sink, or adding a tank or pump brings a permit requirement. Under the code, a "simple system" puts out no more than 250 gallons a day. The same volunteers say to keep graywater off turf and off food plants, root vegetables included. For homes on septic, see septic systems on rural lots.

Can you collect rain from the roof?

Yes. Water Code section 10574 says using rainwater collected from rooftops needs no water right permit, the State Water Board's water rights FAQ confirms. With about 85 percent of the year's rain arriving December through March, a roof tank fills mostly in winter. Rain barrels are not a drinking supply, and they are not the dedicated fire water SLO County Fire may require; see fire water storage and drought on a well.

Sources

1. UC ANR — Use of Graywater in Urban Landscapes in California (2015) — clothes washer conditions; simple systems
2. UC Master Gardeners of SLO County — Graywater Irrigation — when permits apply; plant cautions
3. State Water Board — Water Rights FAQs — rooftop rainwater
4. California Building Standards Commission — Codes — 2025 code in force
5. NOAA NCEI — 1991-2020 normals, Paso Robles — 15.26 inches a year