Forever Chemical Levels in US Drinking Water May Be More Than Twice as High as Reported

Toxic contaminants known as per- and polyfluoroalkyl substances (PFAS) have become ubiquitous in our lives. Nicknamed “forever chemicals,” they resist breaking down in the environment and have been found virtually everywhere—including community water systems. A new study suggests the U.S. may be underestimating PFAS levels in its drinking water by roughly half. The findings, published today in the journal Cell Reports Sustainability, point to a significant gap in PFAS reporting. By counting PFAS levels that fall below minimum reporting thresholds as zero, current methods capture only 44% of the average concentration of 25 types of PFAS in community water systems, the study finds. “‘Below the reporting limit’ does not mean ‘zero,’” first author Gehendra Kharel, an associate professor of environmental and geological sciences at Texas Christian University, told Gizmodo in an email. “About 98% of the roughly 1.86 million individual PFAS test results in the January 2026 dataset were below reporting limits. Those records still carry information: Each one says the concentration was somewhere between zero and the limit.” Revealing a hidden data gap The Environmental Protection Agency (EPA) monitors PFAS levels in U.S. water systems because scientists believe these chemicals could be harmful to human health. In recent years, studies have linked certain levels of PFAS exposure to a wide range of conditions, including some cancers, reproductive issues, hormonal disruptions, birth defects, immunodeficiencies, and high cholesterol. In January, the EPA released monitoring data for 29 types of PFAS across about 10,000 water systems. A subsequent analysis by the Environmental Working Group found that some 176 million Americans are using drinking water that contains PFAS, but most individual test results in the dataset fall below the EPA’s minimum reporting levels (MRLs) and are therefore recorded as “<MRL,” which is treated as zero. To understand how this affects estimates of how much PFAS is actually present in U.S. water systems, Kharel and his colleagues ran their own analysis. They used a statistical method to estimate PFAS concentrations in samples recorded as <MRL, running 1.86 million PFAS test results from 9,991 community water systems through computer models to generate 500 estimates for each below-limit value. Their analysis covered all 25 types of PFAS detected at least once in the EPA’s dataset. The researchers used their results to produce a national estimate of PFAS occurrence, then compared that estimate with one based on reporting that treated below-limit results as zero. They found that the conventional approach captured just 44% of their primary model’s estimate. To be clear, “the central finding is a model-based estimate of PFAS occurrence, not a measurement, and the study does not determine whether anyone’s water is unsafe,” Kharel said. Improving the accuracy of PFAS data Kharel emphasized that below-limit results should remain clearly labeled as such. These limits exist so that people know when PFAS levels could be hazardous to human health. He noted, however, that agencies could report which chemicals were tested, the reporting limits, and how often results fell below them. “When publishing overall averages, they could show estimates that account for below-limit results alongside averages that count them as zero, with uncertainty clearly explained,” he added. More sensitive testing could also reduce the amount of PFAS missed by standard reporting methods. For example, lowering the reporting limits for PFOA and PFOS—two common types of PFAS—allowed conventional reporting methods to capture a much greater share of the model estimate Kharel and his colleagues produced. He hopes this framework will help utilities and researchers explore how below-limit results affect data summaries and identify where further testing might be useful. “For communities, the practical message is to ask what ‘not detected’ means in their report, which chemicals were tested, and what reporting limits were used,” he said.