Sonoma County, California: drinking water report. Sonoma County – Santa Rosa and the wine country north of San Francisco – serves about 490,000 residents.
Sonoma County – Santa Rosa and the wine country north of San Francisco – serves about 490,000 residents. The Sonoma County Water Agency supplies wholesale water from the Russian River, while numerous smaller systems serve communities with local groundwater or small surface water sources. The Russian River watershed is the county's lifeline, but it faces competing demands from agriculture, urban use, and endangered salmon habitat.
The Russian River provides a relatively clean surface water source, but agricultural activity – including viticulture – and rural septic systems contribute nutrients and bacteria to the watershed. Wildfire has also emerged as a water quality factor. The 2017 Tubbs Fire and 2019 Kincade Fire burned through portions of the watershed, releasing ash and debris that affected source water quality for months afterward.
UCMR5 data shows low-level PFAS detections in some county systems. Sonoma County's Charles M. Schulz Airport is a potential PFAS source. According to the California SWRCB, three public water systems in the county reported PFAS above notification levels during 2024 monitoring.
Wildfire and drought are increasingly relevant to water quality and supply in Sonoma County. Post-fire water quality can be affected for months as debris flows into reservoirs.
Check your water for current data in your area. Activated carbon filters handle taste and some PFAS; reverse osmosis provides broader protection. Our water filter guide covers options. Pull your detailed report, and visit our California page for statewide data.