Sonoma County, CA Landscaping Rules: Rainwater Harvesting (2026)

Sonoma County treats rainwater harvesting favorably. Basic above-ground rain barrels and cisterns used to capture roof runoff for outdoor landscape irrigation are broadly allowed and typically do not require a permit, consistent with California law that exempts simple rainwater catchment from licensing. For larger or potable systems, the County took a notable step: in January 2017 Permit Sonoma (then PRMD) adopted Appendix K of the California Plumbing Code, which for the first time lets unincorporated-county homeowners and businesses legally build systems that capture rainwater for potable uses such as drinking and cooking. Those potable systems do require a permit, and approval depends on factors including allowable roofing material, maintenance/inspection/monitoring, and minimum water-quality requirements. Closely related is graywater reuse, which Permit Sonoma regulates under delegated authority from the Regional Water Quality Control Board: a clothes-washer (laundry-to-landscape) system needs a building/plumbing permit but no septic permit, while 'simple' and 'complex' graywater systems require both a septic permit and a plumbing permit plus design review and inspection. Graywater is water from showers, tubs, bathroom sinks, and washing machines - not toilets, kitchen sinks, or dishwashers - and may be routed to the landscape to offset irrigation.