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.”

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.

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