California Surface Water Tests Find Half of Samples Had ‘Forever Chemicals'
Harmful “forever chemicals” have been detected in half of the surface-water samples from California reviewed in a new analysis by the Environmental Working Group (EWG).
Pesticides containing per- and polyfluoroalkyl substances (PFAS) may have detrimental and wide-ranging impacts on health.
Surface water is a major source of drinking water in the state, with some estimates finding that 82 percent of the water
supplied for domestic use comes from rivers, lakes, reservoirs, and other sources.
It comes amid mounting concern about the availability of water in the state, as California’s system is currently built to transport water hundreds of miles from sources like the Colorado River and the Sacramento-San Joaquin Delta-both of which have been significantly strained by climate change.
Where in California Were PFAS Detected?
As part of its analysis, the EWG reviewed four subsets of data, including the 2025 Surface Water Database, or SURF, which surveyed 4,158 samples of surface water spanning 2020 to 2023, across Butte, Colusa, Imperial, Merced, Monterey, San Luis Obispo, Santa Barbara, Stanislaus, Sutter, and Yolo Counties.
Notably, data for Fresno and Kern Counties, where PFAS pesticide applications are the highest in the state, was not reported in the agricultural surface water or sediment monitoring studies within SURF. The EWG said this suggested “a concerning gap in the state of California's testing of PFAS in surface water.”
The EWG found that there was higher overall detection frequencies of PFAS pesticides in surface water in San Luis Obispo (mean detection frequency of 23 percent) and Monterey (22 percent) Counties than the other eight covered.
Bifenthrin, an insecticide containing PFAS, was detected in all 15 samples from San Luis Obispo, and in 88 percent of samples from Stanislaus County.
In Butte and Colusa counties, the 10 most highly detected PFAS pesticides across all samples were detected in under 10 percent of those in the two counties.
PFAS Pesticides-What Are The Concerns?
PFAS chemicals are a group of thousands of different substances widely used in various industries and consumer products, such as nonstick cookware, waterproof clothing, stain-resistant furniture, and many others, even smartwatch wristbands.
Further research has revealed the potential harm the substances pose to public health, and the chemicals are now classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC). Since the classification, research has continued to unravel their potential health risks, such as thyroid disease, liver disease, weakened immunity and many other health problems.
PFAS chemicals do not break down naturally in the environment, and California uses 2.5 million pounds of PFAS a year on its farmland, which means that significant amounts of these chemicals are being pumped into the state’s environment, and staying there.
The EWG previously shared a study showing that more than 50,000 lifetime cancer cases in the U.S. could be prevented if drinking water treatment were developed to be able to handle a “multi-contaminant approach, tackling several pollutants at once.”
It means that these chemicals can find their way into drinking water sources and wastewater. PFAS chemicals can also pass through many traditional water filtering systems, as only advanced, and more expensive, measures can effectively remove them from water.
As overall sampling data is limited in size and scope, the EWG said that PFAS contamination from pesticide use is “likely more widespread than the data currently suggest.”
The EWG added that their findings highlight the “need for much more extensive environmental monitoring.” It also called for California “to phase out the use of these chemicals on crops.”
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This story was originally published May 28, 2026 at 9:26 AM.