General information on PFOS, PFOA, PFBS, PFHxS, and GenX is below. Details about Cal Water’s position are available on the Leadership on PFAS page.


The most commonly found substances within the PFAS family of compounds are PFOS, PFOA, PFBS, PFHxS, and GenX. These are manmade compounds that have been used to make carpets, clothing, fabrics for furniture, paper packaging for food, and other materials (e.g., cookware) that are resistant to water, grease, or stains. They are also used for firefighting at airfields and in a number of industrial processes.

In June 2022, the U.S. Environmental Protection Agency announced reduced Health Advisory (HA) levels of 0.02 parts per trillion (ppt) for PFOS and 0.004 ppt for PFOA. The prior HA level was 70 ppt for PFOS/PFOA combined. EPA also established HAs for PFBS of 2,000 ppt and GenX of 10 ppt.

HAs are non-enforceable, non-regulatory guidelines under which there is no expected risk to health to all people, including sensitive populations, over a lifetime of exposure. The advisories, which offer a margin of protection, also take into account exposure through other sources beyond drinking water. However, they do not take into account technological and economic feasibility of testing and treatment. The HAs are expected to help inform EPA’s eventual regulation, as it sets a draft maximum contaminant level for PFAS compounds later this year.

Subsequently, on October 31, 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. This is a new compound within the PFAS family now being regulated.

The State Water Resources Control Board’s Division of Drinking Water has not changed its response levels for the 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).

How Cal Water is Protecting Our Customers

Protecting our customers’ health and safety is our highest priority, and Cal Water is committed to complying with all standards set by the public health experts. While there is no state or federal maximum contaminant level yet for PFAS compounds, we are following recommendations from regulators, and even went beyond by testing every active source in our systems. Although not required by the state, we believed it was the right thing to do. In cases where detections were above the levels at which state public health experts have recommended water suppliers take action (the response level), we took the affected sources out of service to safeguard customers until treatment was/can be installed.

Additionally, we are analyzing how these new HAs affect our water supply sources; however, currently approved EPA testing methods do not detect down to the new HA levels. As the EPA develops more sensitive testing methods, we will utilize those in our monitoring program.

Studies indicate that long-term exposure to PFAS over certain levels could have adverse health effects, including developmental effects to fetuses during pregnancy or breastfed infants; cancer; or liver, immunity, thyroid, and other effects. Potential health impacts related to PFAS compounds from all sources (which also include food wrappers, firefighting foam, and non-stick cookware, for example) are still being studied, and research is still evolving on this issue. As such, we will continue monitoring the development of an MCL for PFOS and PFOA, the two most common compounds, at the state and federal level, and will comply with any regulations eventually set.

We believe a comprehensive approach is needed to properly address the situation. We’ve encouraged the EPA to establish a consistent, science-based standard as quickly as feasible, and strongly supported state legislation that will prohibit the sale and use of certain products that contain PFAS, require the certification of accurate testing methods for PFAS, and establish a publicly accessible database that houses the sources of PFAS entering water supplies. We have also filed a lawsuit to hold the manufacturers of the compounds responsible and prevent our customers from having to bear the costs of treatment.

This does shed light on the importance of protecting our water resources. While we are doing our part to treat the water and meet the standards the public health experts have set, it’s important that our population as a whole focuses on being good stewards of the environment and takes steps to prevent impacting the water supply.

More information on PFOS and PFOA specifically is available at:

Common Names

PFOS: perfluoroctanesulfonic acid and perfluoroctylsulfonic acid

PFOA: perfluorocaprylic acid, perfluoroctanoic acid, and perfluoroheptanecarboxylic acid

PFBS: perfluorobutane sulfonic acid and potassium perfluorobutane sulfonate (together)

PFHxS: perfluorohexane sulfonic acid

GenX: hexafluoropropylene oxide dimer acid & its ammonium salt