Most of us assume the water from the kitchen tap is checked, measured and safe.
Few people open the annual water quality report their utility sends out. Fewer still think the figures in it might be missing something.
A US-wide analysis published in Cell Reports Sustainability on October 23, 2026 suggests that the official numbers may understate real exposure by about half.
Researchers at Texas Christian University pulled 1.8 million PFAS test results from 9,991 community water systems.
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They estimated the actual average at 5.2 nanograms per liter for the six PFAS now regulated by the US Environmental Protection Agency.
The figure reported under standard methods comes out at 2.6 ng/L. Nearly half of the average concentration gets lost before anyone sees the number.
PFAS, short for per- and polyfluoroalkyl substances, are a family of man-made chemicals used for decades in nonstick coatings, stain-resistant fabrics, firefighting foam and food packaging.
They break down very slowly in the body and the environment, which is why they are nicknamed forever chemicals.
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Why the official tests may miss half of what is there
The gap is not a measurement error. It is a reporting rule.
When a lab tests tap water for PFAS, each chemical has a minimum reporting level. Anything below that threshold is logged as "not detected".
In the national dataset analyzed by the Texas team, 98 percent of individual PFAS results fell below that reporting line. Under standard methods, those readings get counted as zero when averages are calculated.
The TCU authors applied statistical models designed for data where most results sit below the detection limit.
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On that basis, current reporting captures only about 44 percent of the average combined PFAS concentration across the water systems studied.
Lead author Gehendra Kharel is an associate professor of environmental and geological sciences at TCU. In a statement from the university, he described the core issue.
"When the levels of these chemicals are below our reporting limit, it's often treated as zero when we calculate how widespread they are."
His team's method, he added, gives water agencies and utilities a way to account for that difference.
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What the finding means for the EPA limit and your health
The context matters. The EPA finalized its first enforceable PFAS drinking water standards in April 2024. The rule set a maximum of 4 nanograms per liter for the two best-known compounds, PFOA and PFOS.
The study's estimated national average of 5.2 ng/L for the six regulated PFAS already sits above that 4 ng/L line. Compliance, however, is still measured utility by utility, not against a national average.
According to the US Environmental Protection Agency, PFAS exposure has been linked to a higher risk of prostate, kidney and testicular cancer.
The agency also lists reduced immune response to vaccines, interference with the body's natural hormones, higher cholesterol and developmental effects in children.
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Individual exposure depends on your local water source, the age of your pipes and whether your utility already treats for PFAS. The annual Consumer Confidence Report that each US utility sends to customers lists the latest PFAS results for your system.
For households that want to cut exposure at the tap, a home filter certified for PFAS reduction under NSF/ANSI standards 53 or 58 is one option.
Under the EPA's final rule, public water systems have until 2027 to complete initial PFAS monitoring and until 2029 to put treatment in place where levels exceed the limits.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.