Pipe with message reading finished water.

Water Quality

The Zone 7 Standard

Zone 7 continued to provide high quality treated drinking water to 266,000 and businesses, in partnership with our retailers. Our water not only met, but often performed better than state and federal health standards to meet our own more stringent internal water quality targets.

30,042 Water Tests in 2021-2022 fiscal year

5 Lab Staff

172 Different contaminants tested

31 Different analytical methods

PFAS: Proactive monitoring and regulatory compliance

Per and Polyfluoroalkyl substances (PFAS) are chemicals that are prevalent in the environment, that were once commonly used in many consumer products. These chemicals are considered “contaminants of emerging concern” as they are being detected in ground and surface water throughout the environment. However, because their use is so common, there are multiple paths to human exposure in our everyday lives, not just water. PFAS may be found in food wrappers, carpet, rain jackets, or building materials used in the construction of your home. In short, PFAS are everywhere.

PFAS Sources

Over the past several years, the science on PFAS and its impacts on the environment and public health have prompted regulatory actions. The USEPA  is planning to regulate two of the PFAS in drinking water, Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), by the end of 2023. 

The California State Water Resources Control Board is also in the process of developing Public Health Goals (PHGs) for PFOA and PFOS, which is the first step in establishing Maximum Contaminant Levels (MCLs) for these PFAS. Final PHGs are expected in 2023 and once finalized, it will be approximately 2 to 3 years to set Maximum Contaminant Levels (MCLs). Meanwhile, the State has issued drinking water advisory levels for four PFAS (including PFOS and PFOA) and is evaluating five additional PFAS found throughout the state. 

Perfluorooctanesulfonic acid (PFOS)
Perfluorooctanoic acid (PFOA)
Perfluorobutanesulfonic acid (PFBS)
Perfluorohexane sulfonic acid (PFHxS)
Notification Level
Response Level

Zone 7 has been proactive in monitoring for PFAS in water supplies well before any requirements took effect because we know PFAS tend to accumulate in groundwater and are commonly found in groundwater sources throughout the developed world. Fortunately, there have been no detections of PFAS in our imported surface water supplies, which make up the majority of the Tri-Valley region’s water. In addition, two of our ten groundwater wells have not had any detections of PFAS either. However, eight groundwater wells have had some detection levels. Affected operating wells that do not have any current treatment options are taken out of service. Water from affected wells that do have treatment options is blended and/or treated at existing facilities so they fall below the applicable Response Levels before distribution, ensuring that water delivered to our customers meets our high standards.  

In order to proactively manage and treat PFAS in affected wells, Zone 7 is in the process of design and construction of two new PFAS treatment facilities at the Stoneridge Well and the Chain-of-Lakes (COL) wellfield to ensure compliance with applicable PFAS Response Levels and the anticipated MCLs.  

Zone 7 continues to investigate sources of PFAS contamination and how the PFAS plume could be moving in the groundwater basin under various operating scenarios and PFAS management tools.  

The safety of our community’s water supply is our number one priority. Our community can be assured that all water delivered to our customers meets regulatory standards and recommended guidance levels. 

Zone In On
What You Can Do

Source water protection for surface water is everyone’s responsibility! You can help protect our surface water by disposing of trash properly and reporting spills, ensuring our waterways stay clean and free of pollutants. To get helpful tips and tricks for using less toxics options in your home and garden, visit the Clean Water Program website.


Call (925) 454-5000 during regular business hours, or (925) 447-6704 ext. 1 after regular business hours 

Strategic Goals

Water Reliability