A nationwide analysis of nearly 1.9 million water test results suggests federal reporting methods may substantially underestimate concentrations of potentially harmful forever chemicals by treating low-level detections as zero.
By yourNEWS Media Newsroom
Americans may be exposed to substantially higher concentrations of potentially harmful chemicals in drinking water than federal monitoring reports indicate, according to new research suggesting conventional reporting methods account for less than half the estimated amount of certain persistent contaminants in public water systems.
The study, reported by Gizmodo on Oct. 23, found that commonly used methods for calculating concentrations of per- and polyfluoroalkyl substances, known as PFAS, captured approximately 44% of the average levels estimated through statistical modeling. The findings suggest actual concentrations could be more than twice the amounts reflected in conventional calculations.
Researchers from Texas Christian University analyzed approximately 1.86 million individual test results collected from 9,991 community water systems across the United States. Their findings, published in the journal Cell Reports Sustainability, raise questions about how federal agencies interpret laboratory measurements that fall below established reporting thresholds.
PFAS are a large group of synthetic chemicals used for decades in products including nonstick cookware, water-resistant clothing, cosmetics, food packaging and firefighting foam. Often called forever chemicals, they break down extremely slowly and can accumulate in the environment.
Exposure to certain PFAS has been associated with increased risks of some cancers, elevated cholesterol, reproductive and developmental problems, hormonal disruptions and reduced immune responses.
The Environmental Protection Agency monitors PFAS contamination in public drinking water systems, but researchers identified a significant limitation in how results are commonly summarized.
Laboratories use minimum reporting levels to determine the smallest concentrations of individual chemicals they can reliably quantify. When a sample contains a PFAS concentration below that threshold, the result is generally recorded as below the reporting limit rather than assigned a precise numerical value.
In conventional calculations, those results are sometimes treated as zero, potentially excluding chemicals that are present at concentrations too low for reliable measurement.
Gehendra Kharel, an associate professor of environmental and geological sciences at Texas Christian University and the study’s lead author, explained that results below the reporting threshold do not necessarily indicate an absence of contamination.
“‘Below the reporting limit’ does not mean ‘zero,’” Kharel told Gizmodo. “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 researchers examined the EPA’s January 2026 monitoring dataset, which included testing for 29 PFAS compounds across approximately 10,000 water systems.
Of those substances, 25 were detected at least once and included in the researchers’ statistical analysis.
Using a modeling approach designed to account for measurements below laboratory reporting limits, the researchers generated 500 possible concentration estimates for each below-threshold result.
They then compared their estimated national average concentrations with calculations that treated all below-limit results as zero.
The conventional method captured approximately 44.1% of the average combined PFAS concentration estimated by the primary model, indicating that existing reporting practices could underestimate overall chemical occurrence by more than half.
The findings do not mean every public water system contains twice its reported concentration of PFAS. Instead, they illustrate how national estimates can change when researchers account for chemicals that may be present below laboratory reporting thresholds.
Kharel emphasized that the results represent statistical estimates rather than direct measurements of previously undetected contamination.
“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,” he said.
The distinction is important because drinking water safety depends on the concentrations of specific PFAS compounds, their toxicological characteristics and applicable regulatory limits.
In April 2024, the EPA established enforceable drinking water standards for several PFAS, including limits of 4 parts per trillion for two widely studied chemicals, perfluorooctanoic acid, or PFOA, and perfluorooctane sulfonic acid, or PFOS.
The standards were designed to reduce exposure to chemicals associated with serious health concerns. However, the broader PFAS category includes thousands of substances, many of which remain less extensively studied.
The new research also follows earlier findings suggesting widespread contamination of American drinking water.
An Environmental Working Group analysis of federal monitoring information estimated that approximately 176 million Americans receive drinking water containing detectable PFAS. That figure represents an estimate of populations served by affected systems, rather than a count of individuals whose exposure has been directly measured.
The researchers say improved reporting methods could provide a more complete picture of contamination without changing the underlying laboratory results.
Rather than treating every below-threshold measurement as zero, water monitoring agencies could publish statistical estimates alongside conventional averages, clearly identifying the uncertainty associated with concentrations that laboratories cannot reliably quantify.
“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,” Kharel said.
The study also found that improving laboratory sensitivity could narrow the difference between reported and estimated contamination.
When reporting thresholds were lowered for PFOA and PFOS, conventional calculations captured a substantially larger proportion of the concentrations estimated through the researchers’ modeling approach.
The findings suggest more sensitive testing could help regulators identify low-level contamination that current reporting practices may overlook.
Kharel recommended that consumers examine their local water utility reports to determine which PFAS were tested, what laboratory reporting thresholds were applied and how results below those limits were classified.
“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.
The researchers hope their methodology will help water utilities, public health officials and environmental scientists identify gaps in existing monitoring programs and prioritize additional testing.
Although the study does not establish that drinking water systems are violating federal safety limits, it suggests national contamination estimates may be incomplete when measurements below laboratory reporting thresholds are excluded.
The findings underscore the importance of distinguishing between chemicals that are genuinely absent from drinking water and those that may be present at concentrations existing testing methods cannot reliably quantify.
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