Levels of PFAS chemicals in U.S. drinking water may be as much as twice as high as official estimates, according to a new study. The problem, the researchers say, is that current reporting methods may capture only 44% of the average concentration of 25 PFAS elements in community water systems.
“When the levels of these chemicals are below our reporting limit, it’s often treated as zero when we calculate how widespread they are,” said Gehendra Kharel, first author of the study at Texas Christian University in Fort Worth, in a news release. “We set out to understand how treating those results as zero changes the picture of PFAS occurrence in drinking water.”
Under the Safe Drinking Water Act, the Environmental Protection Agency (EPA) requires public water systems to monitor the levels of 29 PFAS elements in drinking water. These chemicals can persist in the environment over a long time, and previous research has linked PFAS exposure to many health issues, including cancer, liver damage, and developmental problems in children.
In January 2026, the EPA published a near-complete release of monitoring data from water systems across the country, showing that at least 3,500 water systems had PFAS in their public water supplies.
While an analysis by the Environmental Working Group suggests that some 176 million Americans use water from systems where at least one type of PFAS was detected, most individual PFAS test results in the dataset fall below the EPA’s minimum reporting levels (MRLs) and thus are recorded as “<MRL.”
“Minimum” doesn’t mean zero
The researchers at TCU say that by counting PFAS levels that fall below minimum reporting levels as zero, current reports capture only 44% of the average concentration of 25 PFAS in community water systems. The study is publishing today in the journal Cell Reports Sustainability.
The MRL generally means a concentration that most laboratories can reliably measure and report, but it doesn’t suggest that the water tested is PFAS-free or that it’s safe, Kharel said. But these data points are often treated as zero when agencies and researchers summarize average PFAS levels in drinking water.
“When a water quality report says ‘not detected,’ that means below the reporting limit, not zero,” says Kharel. “Our method gives water agencies and utilities a way to account for that difference, so they can see where more testing would help and be clearer about what they do and do not know.”
The EPA has set legally enforceable limits covering six PFAS in drinking water, including perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), that have been linked to serious health problems. When counting below-limit results as zero, the national average concentration is about 2.6 nanograms per liter in drinking water for the six chemicals. But the team’s model estimates that, in reality, the average could be 5.2 nanograms per liter
“Our study only examines how PFAS measurements are summarized,” says Kharel. “It does not establish that every below-limit result poses a health risk.”
Although these values are model-generated predictions rather than measurements of actual concentrations below reporting limits, Kharel says the findings could help provide a more complete picture of PFAS levels in US drinking water and improve how environmental monitoring data are interpreted.
How did it happen?
There’s no question that public water supplies contain PFAS. How it got there and how to get rid of it are open to debate.
Common sources of PFAS contamination include industrial plans, military bases and airports, landfills and contaminated soil and groundwater.
Documented health risks include higher cholesterol levels, reduces immune response to some vaccines, liver damage, development effects in children, increase risk of kidney and testicular cancer and pregnancy-related high blood pressure.
What to do?
Consumers can check the quality of their water by checking EPA data. For contaminated water, activated-carbon and reverse-osmosis filters can reduce some PFAS chemicals. Boiling water has no effect on PFAS.
The chemicals have been in common use for decades and older Americans have been exposed to them during that time. There’s no changing history but home filters and efforts to clean up public water supplies could be beneficial for younger consumers.