The EPA’s Fifth Unregulated Contaminant Monitoring Rule — the largest federal drinking water testing program ever conducted for PFAS — is nearly complete. With 95% of results now published, the data confirms what researchers have long suspected: PFAS contamination in American drinking water is not rare, not localized, and not limited to communities near obvious sources like military bases or chemical plants.
As of March 2026, here’s what the data shows and what it means for the millions of Americans whose water has been tested.
The Numbers
The EPA published its eleventh UCMR 5 data release in February 2026, covering results received through January 15, 2026. The key findings:
- 10,299 public water systems have reported results
- ~1.9 million individual sample results have been analyzed
- 3,539 water systems have detected at least one PFAS compound above reporting limits
- That’s roughly 1 in 3 systems tested showing detectable PFAS contamination
- The final data release is expected in fall 2026
These numbers represent approximately 95% of the total results the EPA expects to receive. The remaining 5% — primarily from smaller systems that were sampled later in the 2023–2025 testing window — will be included in the final release.
What Was Tested
UCMR 5 required monitoring for 29 PFAS compounds plus lithium, using EPA analytical methods 533 and 537.1. These methods can detect PFAS at single-digit parts per trillion — a sensitivity that was not possible in earlier monitoring cycles.
The program covered:
- All large public water systems serving 10,000 or more people (mandatory)
- A representative sample of small systems serving 3,300–10,000 people (mandatory)
- Some very small systems serving fewer than 3,300 people (voluntary in some states)
Private wells were not included. An estimated 20 million Americans rely on private wells, and many live in areas with known PFAS contamination sources. If you’re on a private well, see our well water testing guide for information on getting your water tested independently.
Most Commonly Detected Compounds
The most frequently detected PFAS compounds in UCMR 5 data align with what researchers expected — legacy compounds from decades of industrial use and firefighting foam:
PFOS (Perfluorooctane Sulfonic Acid)
The most commonly detected compound. PFOS was the active ingredient in 3M’s Scotchgard fabric protector and a key component of AFFF firefighting foam. Despite being phased out of U.S. production by 2002, PFOS persists in groundwater and surface water indefinitely. The EPA set a maximum contaminant level (MCL) of 4 ppt for PFOS under the 2024 PFAS drinking water rule.
PFOA (Perfluorooctanoic Acid)
The second most frequently detected compound. PFOA was used in the manufacturing of Teflon and other fluoropolymer products. Classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC) in 2023, PFOA has an MCL of 4 ppt. For detailed health information, see our PFAS contaminant profile.
PFBS (Perfluorobutane Sulfonic Acid)
A short-chain PFAS that replaced PFOS in many applications. PFBS is more mobile in groundwater than its longer-chain predecessors, meaning it spreads farther from contamination sources. It’s regulated under the Hazard Index approach — though the future of that standard is currently in litigation.
HFPO-DA (GenX Chemicals)
The replacement for PFOA in fluoropolymer manufacturing, produced primarily by Chemours. GenX has been detected in water systems near manufacturing facilities, particularly in North Carolina and the Delaware Valley. The original MCL of 10 ppt is part of the ongoing regulatory dispute.
Where Contamination Is Highest
UCMR 5 data reveals geographic patterns that reflect the history of PFAS use in the United States:
Military and Airport Communities
Water systems near military bases, airports, and fire training facilities show some of the highest PFAS concentrations. The Department of Defense has identified over 700 installations with known or suspected PFAS contamination from AFFF firefighting foam use.
Industrial Corridors
Communities near chemical plants, semiconductor manufacturers, textile mills, and other PFAS-using industries show elevated detections. Notable clusters include North Carolina’s Cape Fear region (Chemours/GenX), West Virginia and Ohio along the Ohio River (legacy DuPont operations), and Michigan’s industrial belt.
Wastewater-Influenced Systems
Water systems that draw from rivers and lakes receiving upstream wastewater discharge show consistent PFAS detections. Conventional wastewater treatment does not remove PFAS, so treated effluent carries these chemicals downstream to the next community’s intake.
Groundwater-Dependent Systems
Contamination in groundwater-fed systems is particularly concerning because PFAS in groundwater can persist for decades or longer without natural degradation. These systems often serve smaller communities with fewer resources for treatment upgrades.
Check the PFAS contamination map to see detection patterns across the country, or search your city to see specific UCMR 5 results for your water system.
How UCMR 5 Data Shaped Federal Policy
The UCMR 5 results directly informed — and continue to influence — federal PFAS regulation:
The 2024 Drinking Water Standards
The EPA used early UCMR 5 data to justify the first-ever national PFAS drinking water standards, finalized in April 2024. The widespread detections demonstrated that PFAS contamination was a national problem requiring a national regulatory response, not just site-specific cleanup actions.
The Regulatory Rollback Debate
The same data is now central to the litigation over the Trump EPA’s partial rollback of those standards. Environmental groups have cited UCMR 5 results showing widespread detections of GenX, PFHxS, and PFNA as evidence that rescinding standards for these compounds would leave millions of Americans without protection.
State-Level Action
Several states have used UCMR 5 data to set their own PFAS standards — in some cases stricter than federal limits. New Jersey, Michigan, New Hampshire, Vermont, and Massachusetts have all established state-level PFAS MCLs, with some covering compounds not addressed by the federal rule.
The Bigger Picture: 9,700+ Known PFAS Sites
UCMR 5 is the largest single source of PFAS data, but it’s not the only one. The Environmental Working Group’s contamination tracker now documents 9,728 known PFAS contamination sites across all 50 states — combining UCMR 5 results with Department of Defense data, state-level testing, and industrial site investigations.
That number will continue to grow as the remaining 5% of UCMR 5 results come in and as states expand their own testing programs.
What You Can Do
Check your water
Search your city on WaterVerge to see UCMR 5 results integrated with other water quality data. We show which PFAS compounds were detected, at what concentrations, and how they compare to federal MCLs and health advisory levels.
Understand the contaminants
Visit our PFAS contaminant profile for health effect information, or read the PFAS in Drinking Water guide for a comprehensive overview of the science, regulation, and filtration options.
Filter if needed
If your water system shows PFAS detections above 4 ppt, consider home filtration. Reverse osmosis systems remove over 90% of PFAS. NSF P473-certified pitcher filters — including Clearly Filtered and Epic Pure — are effective and affordable. See our best water filter pitchers guide for specific recommendations.
Stay informed
Set up water alerts for your area to receive notifications about water quality changes, violations, and boil water notices. As new UCMR 5 data is published — and as the regulatory landscape continues to shift — WaterVerge will update city-level reports automatically.
What’s Next
The final UCMR 5 data release is expected in fall 2026, completing the most comprehensive picture of PFAS in American drinking water ever assembled. The EPA will use this data to evaluate whether additional compounds need regulation and to assess compliance needs for the thousands of systems that will need treatment upgrades.
Meanwhile, the next generation of monitoring — likely UCMR 6 — is expected to expand testing to additional emerging contaminants beyond PFAS. The EPA has not yet announced the scope or timeline for UCMR 6.
Related Coverage
- EPA PFAS Drinking Water Rule: What Survived and What Got Cut — the regulatory battle over PFAS standards
- PFAS in Drinking Water: A Practical Guide — full guide to PFAS science and filtration
- PFAS Contaminant Profile — detection data and health effects
- PFAS Contamination Map — interactive map of PFAS detections nationwide
- Best Water Filter Pitchers for 2026 — tested filters for PFAS removal