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Water Quality

Water drop

Our core mission is to provide fresh, high-quality drinking water at a reasonable price. Our local water supply means you can be sure your water is clean, fresh and sustainably sourced. Our water meets or exceeds all state and federal drinking water standards, and costs most customers about two cents per gallon.

Marin Water takes many steps to ensure the water delivered to your service line is of the highest quality including managing our watershed lands and reservoirs, treating the water, operating and monitoring a complex distribution system, and maintaining and upgrading our facilities. Every year, we release a Water Quality Report that provides information about our water sources, treatment process, water testing results, and more.

After we process and deliver clean drinking water to your home, your household may pose water quality risks as a result of what is called backflow.

Cross-connections, a temporary or permanent location between public drinking water and a consumer's water system, could potentially introduce contamination or pollution into the public or private drinking water system.

​Irrigation systems, hose bibs, boilers, radiant heat systems, wells, docks, ponds, fountains, pressure boosting systems, pools, spas, graywater systems, rainwater collection systems, reclaimed water, and solar heating systems are just a few examples of hazards that need to have backflow protection.

Backflow Preventers Protect Water Quality

The installation of a backflow preventer will protect drinking water systems from possible contamination.

​There are four types of assemblies. If the district has done a survey of your residence or business you will receive a letter letting you know which type of assembly is best suited for you and the location of where it must be installed. There are many brands to choose from, but your assembly must be on Marin Water's list of approved backflow assemblies formulated by the University of Southern California Foundation for Cross-Connection Control and Hydraulic Research.

Having a backflow preventer installed at your meter protects only the public water system. There may be unprotected cross-connection issues within your property. You may email us at if you have any questions or call 415-945-1488. Or you may refer to our list of Certified Testers to find a cross-connection specialist that can meet with you and conduct an in-depth survey of your home or business.

​Scheduling annual inspections is required in order to ensure the public drinking water system is protected from possible contaminants. A visual inspection of an air gap is sufficient, but backflow assemblies must be tested by a Certified Backflow Prevention Assembly Tester using a properly calibrated gauge.

Backflow Assembly Testers

Backflow Assembly Testers play a vital role of keeping the public drinking water system safe and clean by preventing backflow. Marin Water relies on backflow assembly testers to submit accurate information in a timely manner.

New Testers

All new testers must submit an online application in order to be added to the approved Marin Water Testers List. After submitting the application, please scan and email copies of current Certifications and Gauge Verification to After we have received all the documents, we will process the application and schedule a hands-on demonstration, held  in April and October. Submit an online application here

Online Test Report

Submit an online test report here.

For more information, please call 415-945-1488 or email us at

Additional Resources

Every year Marin Water cleans some of its water mains to remove built-up sediment so we can maintain the high-quality water you expect from us.

To clean a water main, we turn on select hydrants along a section of the water main. Water comes out of the hydrants with enough velocity to clean the water main. We also collect water quality samples as part of the water main cleaning process to ensure our water meets the highest standards.

During the cleaning process, you may notice water in the streets as well as slight drops in water pressure. After the cleaning, you may notice air in your water lines at first, or a brief discoloration of water in your own plumbing. If you notice these effects, we recommend running cold water for a short time to remove any loose sediment in the pipeline that runs from our water main to your home. 

For questions or additional information about water main cleaning in your area, contact us at 415-945-1438 or email us at

Fresh From the Source

We are proud to provide 100% locally sourced water to more than 191,000 residents in central and southern Marin County. About 75% of our water supply originates from rainfall on our protected Mt. Tamalpais watershed and in the grassy hills of west Marin - 22,000 acres in all - with the remaining supply coming from neighboring Sonoma County’s Russian River water system. 

Rainfall from the watershed flows into the district’s seven reservoirs. The water is treated at our treatment plants before traveling through our extensive distribution system, including 908 miles of pipes, 130 storage tanks and 97 pump stations before making its way to your home or business. It takes 24 hours for water to travel from a reservoir to a treatment plant and then through miles of underground mains into your faucet. Your cost for a gallon of water delivered is less than one cent.

Every year the district conducts more than 120,000 water quality and process control tests to ensure your water is safe to drink. This includes ongoing process control testing at our treatment plants as well as laboratory testing of our water samples. When it comes to health and safety, your drinking water is required to meet or exceed all state and federal drinking water standards.

Seasonal Changes

Occasionally, during the warmer months, some customers experience a different taste or odor in their drinking water. Some describe the water as tasting and smelling earthy, musty, or moldy. This is caused by naturally occurring compounds produced by algae in our reservoirs. Algae are a natural phenomenon, particularly during the warm summer months, and are a reminder that our lakes are living water bodies.

During certain times of the year, we may also shift water sources from one reservoir to another to manage our water supply. These operational changes can result in customers noticing changes to the taste and smell of their tap water. These slight changes, which are common in lake water, do not affect the safety of your water. Your water is treated and meets or exceeds all state and federal requirements.

For those who are more sensitive to taste and odor changes, chilling the water during these periods will help reduce the temporary change in taste or smell of your water. For questions or for more information contact us at 415-945-1550 or at