# PFAS in Drinking Water Likely Underestimated by Half, New Analysis Reveals
A new study in *Cell Reports Sustainability* found that PFAS contamination in U.S. drinking water supplies may exceed current estimates by more than 100 percent. The research reanalyzed federal monitoring data and exposed a methodological flaw: when per- and polyfluoroalkyl substances fall below laboratory detection thresholds, federal agencies and water systems treat these results as zero rather than applying statistical estimation techniques.
PFAS are industrial chemicals used in nonstick coatings, food packaging, and firefighting foam. The class contains thousands of compounds, many of which persist indefinitely in soil, groundwater, and human blood. Six PFAS chemicals currently face federal drinking water standards: PFOA, PFOS, PFHxS, PFNA, PFDecA, and GENX.
The U.S. Environmental Protection Agency set maximum contaminant levels for these six compounds in 2024. PFOA and PFOS limits dropped to 4.0 parts per trillion and 4.0 ppt respectively, marking the strictest drinking water standards EPA has ever established. However, the new analysis raises questions about whether current compliance testing accurately reflects real exposure.
When laboratory equipment cannot detect PFAS below certain concentrations (called the method reporting limit, or MRL), the standard practice treats nondetects as absent entirely. Researchers from universities and nonprofit organizations obtained EPA's Second Unregulated Contaminant Monitoring Rule dataset, which tracks PFAS levels across thousands of water systems. They applied survival analysis and maximum likelihood estimation, statistical methods commonly used in environmental epidemiology, to estimate likely concentrations of compounds reported as "not detected."
Results showed that estimated total PFAS concentrations in U.S. drinking water approached twice the levels calculated using traditional methods that ignore nondetects. Some drinking water systems showed even larger discrepancies. The findings suggest that compliance testing may underestimate actual PFAS exposure across the nation's water infrastructure.
This matters for two reasons. First, the epidemiological record links PFAS exposure to immune suppression, thyroid disease, kidney cancer, testicular cancer, and reduced vaccine efficacy. The CDC found detectable PFAS in the blood of 97 percent of Americans tested. Second, water utilities face billions in infrastructure costs to remove PFAS. If contamination levels are actually double what current testing shows, treatment priorities and regulatory timelines may shift significantly.
The EPA's 2024 standards require water systems serving more than 10,000 people to comply by January 2029. Smaller systems face deadlines in 2031 and 2032. The agency estimated compliance costs between 1.2 and 3.3 billion dollars over three years for large systems alone.
Industry groups and some state officials have pushed back against stricter PFAS limits, citing treatment costs and analytical challenges. The new study strengthens the case for lower thresholds. It also highlights a broader problem in environmental monitoring: laboratories continually improve detection capabilities, potentially revising our understanding of contamination levels established under older technology standards.
The EPA and drinking water industry have not yet responded to the *Cell Reports Sustainability* findings. Water utilities now face pressure to upgrade testing methods or adopt the statistical approaches used in this reanalysis to ensure their compliance assessments reflect actual resident exposure.