Tap water and supplyGuide

Where Sonoma County tap water comes from

By The Downspout · Updated Oct 11, 2026 · 1 min read Share

Most tap water served by Sonoma Water starts in the Russian River system. It is pulled from the ground beside the river, treated lightly, and piped to your city or district.

The steps

1. Two reservoirs. Lake Mendocino holds up to 118,000 acre-feet. Lake Sonoma holds up to 381,000. Both also serve flood control.
2. The river. The Russian River runs 110 miles and drains 1,485 square miles. Sonoma Water releases reservoir water to meet demand and keep minimum river flows.
3. Collector wells. Six wells sit beside the river. They pull river water through the gravel under it. The agency says this naturally filtered water needs no added treatment.
4. Chlorine and pH. Chlorine is added as a precaution. Sodium hydroxide raises the pH to cut corrosion of lead and copper in indoor plumbing.
5. Pipes. Over 88 miles of pipeline and 18 tanks holding about 129 million gallons send it to cities and districts.

Backups

Sonoma Water also runs three wells in the Santa Rosa Plain, built in 1977 in response to drought, and seven standby wells near the Mirabel collectors.

Who gets it

Sonoma Water says it serves over 600,000 people in Sonoma and northern Marin counties. Your bill comes from your city or district, not from Sonoma Water. Some homes use their own wells instead.

Acre-foot: about 325,851 gallons, the water that covers an acre one foot deep.

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