EPA could be vastly under-reporting PFAS levels in drinking water, study finds
US drinking water could contain double the PFAS levels currently reported by regulators, according to a new study from Texas Christian University.
The study, published in Cell Reports Sustainability, used computer modeling to estimate that the latest reports from the Environmental Protection Agency (EPA) capture only 44% of the average combined concentration of 25 polyfluoroalkyl substances (PFAS) in US water systems.
PFAS, also known as “forever chemicals,” are known to persist in the environment and are linked to some cancers, high cholesterol, reproductive issues and other health problems.
Researchers analyzed more than 1.8 million PFAS measurement records from the EPA’s January 2026 release of monitoring data from water systems across the country. They found most individual PFAS test results in the dataset fall below the EPA’s minimum reporting levels (MRLs).
These data points are often treated as zero when agencies and researchers summarize average PFAS levels in drinking water.
The authors found that 98% of PFAS test results were below the MRL. The MRL generally means a concentration that most laboratories can reliably measure and report. However, the study’s authors argue that this doesn’t mean that the water tested is PFAS-free or that it’s safe.
“Below the reporting limit does not mean zero. Our study shows why that distinction matters when summarizing PFAS concentrations,” said lead author Gehendra Kharel, associate professor of environmental and geological sciences at Texas Christian University.
Kharel and his team used computer models applied to data from the EPA’s Fifth Unregulated Contaminant Monitoring Rule (UCMR 5), a nationwide program that requires public water systems to test drinking water for specific PFAS. They used this dataset to estimate possible concentrations for PFAS records listed below the EPA’s MRL.
They averaged hundreds of data points to come up with an estimate, performing this calculation for all 25 PFAS that had been detected at least once in the EPA’s dataset.
Under the study’s primary statistical model, they found that treating below-limit results as zero captured only 44% of the average combined concentration of the 25 PFAS monitored across 9,991 community water systems.
Jesse Goodrich, assistant professor in the division of environmental health at the University of Southern California, said that while municipal drinking water data explains why certain people have elevated chemical levels, these findings clarify why so many Americans, regardless of location or water source, have detectable PFAS in their blood.
“People traditionally have thought that drinking water is a large source of exposure to different PFAS compounds. And so when you look at the UCMR results, you see a lot of zeros, and that is hard to reconcile based on the human biomonitoring studies, where you see that everyone is actually exposed,” Goodrich said.
The results of this study are model-generated predictions rather than measurements of actual concentrations. However, Goodrich believes the results explain how trace contamination builds up.
“There’s very low levels of PFAS in drinking water, and over time, since compounds have such a long half life, that can add up to measurable, kind of ubiquitous exposure in the population,” Goodrich said.
Kharel believes the study could help provide a more complete picture of PFAS levels in US drinking water and improve how environmental monitoring data are interpreted, bridging the gap between official estimates and the actual level of chemicals in our water.
A conservative approach
Alissa Cordner, co-director of the PFAS Project Lab at Northeastern University, said the EPA takes a more conservative approach by treating unmeasurable chemical samples as zero, which results in the lowest possible contamination estimates.
Cordner argues scientists can use better methods. Instead of assuming zero, researchers often estimate low-level presence by dividing the lab’s detection limit by either two or the square root of two.
“Either of those approaches are going to give you a less conservative and potentially more environmentally relevant measure of what’s actually going on in these samples,” she said.
Kharel recommends that agencies supplement traditional reporting methods by including estimates for below-limit results, alongside clear disclosures of detection limits, the percentage of unmeasurable samples, and margins of error.
“These practices would complement existing compliance procedures, not replace them or change health standards,” he said. Kharel and his team developed PFAS-CAST, an open-source tool designed to let agencies explore this approach with their own monitoring data.
This study comes after another report, which was published by Environment America Research & Policy Center last week, found that PFAS pollute more than 80% of tested US waterways.
In May, the EPA proposed dropping limits for four cancer-linked “forever chemicals” in drinking water established during the Biden administration, prompting concern from scientists who say even low dose exposure to PFAS can be harmful to human health over time.
“PFAS have been shown to impact human health at extremely low levels of exposure,” said Cordner. Just because standard lab tools can’t detect a chemical, “that doesn’t mean everything is zero.”
Featured image: RephiLe waterfor Unsplash+
