Water Quality


Sonoma Water provides quality drinking water to nine cities and water districts in portions of Sonoma and Marin counties. Sonoma Water ensures its drinking water meets all state and federal water quality requirements by performing daily, weekly and monthly tests. 

The U.S. Environmental Protection Agency requires every community water supplier to provide a Consumer Confidence Report to its customers. Sonoma Water provides this report, also known as an Annual Drinking Water Quality Report to our water contractors. Information in this report includes:

  • A summary of the risks of contamination of the local drinking water source.
  • The regulated contaminants found in local drinking water.
  • The potential health effects of any contaminant detected in violation of an EPA health standard. 
  • An accounting of the water system’s actions to restore safe drinking water.
  • An educational statement for vulnerable populations about avoiding Cryptosporidium.
  • Educational information on lead, nitrates, and/or arsenic, in areas where these contaminants may be a concern.

In addition to Sonoma Water’s extensive water quality tests, the cities and water districts that contract to receive this water supply also perform individual water quality sampling and tests. Below are the links to each of the cities’ and water districts’ water quality web pages to learn more about individual testing and results:

Final PFAS National Primary Drinking Water Regulation

On April 10, 2024, the U.S. Environmental Protection Agency (EPA) published regulations that set limits for five individual per- and polyfluoroalkyl substances (PFAS):  PFOA, PFOS, PFNA, PFHxS and HFPO-DA.
The regulation calls for a maximum contaminant level for:

  • PFOS of 4 parts per trillion (ppt)
  • PFOA of 4 ppt
  • PFHxS of 10 ppt
  • PFNA of 10 ppt
  • GenX (HFPO-DA) of 10 ppt

The EPA also set a combined hazard index limit of 1.0 for any combination of PFNA, PFHxS, PFBS and GenX; the hazard index calculation would determine if the levels of these PFAS as a mixture pose a potential risk.

Under the EPA ruling, (Per- and Polyfluoroalkyl Substances (PFAS) | US EPA), public water systems must monitor for these PFAS compounds and complete initial monitoring by 2027, followed by ongoing compliance monitoring and must comply with the regulation within five years.

In October 2022, the California State Water Resources Control Board’s Division of Drinking Water issued a notification level of 3 ppt and response level of 20 ppt for PFHxS. The Division of Drinking Water already had response levels for other PFAS compounds (PFOA: 10 ppt; PFOS: 40 ppt; PFBS: 5,000 ppt) and notification levels (PFOA: 5.1 ppt; PFOS: 6.5 ppt; PFBS: 500 ppt).

Sonoma Water has annually monitored for PFAS compounds for the last five years and is set to begin the required quarterly monitoring in April 2024. Sonoma Water has not found concentrations in the water delivered to our community above the current state response and notification levels nor have we found concentrations above the maximum contaminant levels set by the EPA on April 10, 2024. Sonoma Water will continue to closely monitor the evolving regulations to ensure that we meet or exceed state and federal requirements. 


Frequently Asked Questions:

Where does Sonoma Water get its water from?

Sonoma Water produces water from the Russian River that is pumped from wells about 100 feet below the river bed. This system of pumping is called river bank filtration. Six groundwater wells, also known as collectors, pump the water through natural sands and gravels that act as a filtering system. Sonoma Water does not provide surface water taken directly from a river or lake to its customers.

How does Sonoma Water keep its water clean?

Sonoma Water adds chlorine to its water supply to provide residual disinfection throughout its water transmission system. Sonoma Water also adjusts the pH of its water with sodium hydroxide to address the inherent characteristics of Russian River water that tend to corrode copper plumbing. The quality of drinking water is generally considered in two ways: the presence of contaminants that might cause adverse health effects, and properties of water that affect aesthetics. Contaminants that may cause adverse health effects include inorganic and organic chemicals, and microbiological contaminants. The aesthetic qualities of drinking water include characteristics that make the water unpalatable or bothersome to customers. Examples are hardness, taste, odor, color, temperature and the tendency to discolor plumbing fixtures.

Does Sonoma Water’s transmission system include lead pipes?

No. Sonoma Water's wholesale water transmission system is constructed with underground pipes that are made of concrete lined steel. Contact your local water supplier to learn more about their retail distribution system (see above links).

Why does Sonoma Water adjust the water’s pH?

Excessively high and low pHs can be detrimental for the use of water. High pH causes a bitter taste, water pipes and water-using appliances become corroded or encrusted with deposits, and it depresses the effectiveness of the disinfection of chlorine thereby causing the need for additional chlorine when pH is high. Low pH water can corrode or dissolve metals and other substances. Sonoma Water monitors the level of pH in its water system on a daily basis. The pH level within the water system must achieve an average daily range of 8.2 to 8.6 for 95 percent of all daily average values. To adjust the level of pH Sonoma Water uses Sodium Hydroxide (NaOH), also known simply as caustic soda. Sodium Hydroxide is the most widely used alkaline neutralizing chemical in use in industry today as it is easy to handle and very effective for the neutralization of strong or weak acids. More information on pH is available here.

How old is the water transmission system?

Sonoma Water’s water transmission system varies in age, but elements of it are up to 50 years old. Constant monitoring and water quality testing ensures the pipes are in functional order and ongoing maintenance work is conducted to evaluate and repair leaks or damage before they occur. This type of proactive maintenance work not only reduces health risks associated with leaks but also reduces costs by fixing an issue before it becomes an emergency.

Who monitors Sonoma Water’s water quality reports?

Sonoma Water operates under a water supply permit issued by the State Water Resources Control Board's Division of Drinking Water. This permit requires Sonoma Water to operate and maintain its water supply system in compliance with state water law. This permit includes water quality monitoring requirements and various other conditions and criteria. Sonoma Water consistently meets state and national standards for drinking water quality.

Does Sonoma Water add fluoride to its water?

No. Sonoma Water does not add fluoride.


Water Quality for Private Wells

The County of Sonoma offers water testing for private wells. Call 707-565-4711 or visit the following websites:

Water Quality Resources: