Sonoma County's water supply comes primarily from the Russian River system managed by Sonoma Water (Sonoma County Water Agency), which serves most cities and special districts in the county. Unincorporated areas are served by smaller mutual water companies, private wells, and county service areas. Sonoma County Code Chapter 25B requires private wells to meet permit and metering standards, and the county Board of Supervisors and Sonoma Water issue coordinated drought-stage declarations that trigger outdoor watering bans, day-of-week schedules, and well-pumping restrictions. The state's MWELO (Cal. Code Regs. Title 23, §490) applies to landscape projects of 500 sq ft or more in unincorporated Sonoma County.
Sonoma County is one of California's most drought-sensitive counties. The Russian River and Lake Sonoma (Warm Springs Dam) are the primary supply for Sonoma Water, which wholesales to nine cities and special districts including Santa Rosa, Petaluma, Rohnert Park, Cotati, Sonoma, Windsor, Valley of the Moon Water District, North Marin Water District, and Marin Municipal Water District. Key county-level rules:
SONOMA COUNTY CODE CHAPTER 25B — WELLS: Private well drilling, deepening, and destruction require a permit from Sonoma County Permit Sonoma. Wells must include a meter when located in groundwater-management areas under the Sustainable Groundwater Management Act (SGMA). The Petaluma Valley, Sonoma Valley, and Santa Rosa Plain groundwater basins have adopted Groundwater Sustainability Plans (GSPs) that may restrict new well construction and pumping volumes.
DROUGHT EMERGENCY DECLARATIONS: The Board of Supervisors and Sonoma Water issue coordinated drought declarations (Stage 1–4). During the 2020–2022 drought, the Board declared a drought emergency in April 2021 and called for voluntary 20% conservation, escalated to mandatory restrictions later that year. Typical restrictions during a declared drought: - No outdoor irrigation between 9 a.m. and 7 p.m. - Watering limited to 2 or 3 days per week (odd/even or numbered schedule). - No washing of hardscape (driveways, sidewalks). - Hose nozzles with positive shutoff required. - No new turf in new developments. - Restaurants serve water only on request.
SGMA GROUNDWATER RESTRICTIONS: In the Petaluma Valley, Sonoma Valley, and Santa Rosa Plain groundwater basins (designated medium-priority under SGMA), Groundwater Sustainability Agencies (GSAs) have adopted plans that may require well metering, reporting of pumping, and restrictions on new wells. Property owners in these basins should check with the relevant GSA before drilling.
MWELO: Cal. Code Regs. Title 23, §490 (Model Water Efficient Landscape Ordinance) applies to new or rehabilitated landscapes of 500 sq ft or more in unincorporated Sonoma County. Permit Sonoma enforces it through the building permit process. Turf is capped, water budgets are required, and pressure-regulated drip irrigation with smart controllers is mandatory.
RETAIL PROVIDERS: City restrictions are set by each city (Santa Rosa, Petaluma, Sonoma, etc.) and special districts (Valley of the Moon Water District, North Marin Water District). Unincorporated residents on county service areas (e.g., Russian River CSA) follow Sonoma Water's wholesale-customer guidance.
Violating a drought-stage restriction is enforced administratively by the water purveyor (Sonoma Water customers via the wholesale customer, retail water providers for their service areas) with warnings on the first offense and administrative fines (typically $50–$500 per occurrence) for repeat violations. Drilling or deepening a well without a Permit Sonoma well permit under Chapter 25B exposes the property owner to permit revocation, daily fines, and potential well destruction at owner expense. Failure to meter and report pumping in an SGMA-regulated basin can trigger GSA enforcement and pumping reductions.
See how Sonoma County's water restrictions rules stack up against other locations.
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