The EPA finalized its first-ever legally enforceable limits for PFAS in drinking water in April 2024: 4 parts per trillion for PFOA and PFOS, the two most studied compounds. To put that in perspective, 4 ppt is roughly four drops of water in an Olympic-sized swimming pool. The limit is that low because the EPA determined there is no level of PFOA or PFOS exposure that can be considered fully safe.
The compliance deadline is 2029. In the meantime, the EPA's Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) has tested approximately 10,290 public water systems as of January 2026. What it found was not reassuring.
The National Picture
Nationally, 34.4% of public water systems tested detected at least one PFAS compound. 8.0% of systems had averages above the new EPA Maximum Contaminant Level. The Environmental Working Group's broader contamination mapping puts the total number of PFAS-affected sites at 9,728 nationwide.
But these averages mask enormous state-by-state variation.
The Five Worst States
1. New Jersey: 556 systems above proposed limits
No state in the country has more documented PFAS contamination than New Jersey. The EWG counts 556 water systems with PFAS above proposed federal limits, the highest total nationally by a considerable margin. The detection rate is 81.5% of all tested systems. The highest single sample recorded is 210 ppt, more than 50 times the EPA's 4 ppt MCL.
New Jersey's PFAS history traces to decades of chemical manufacturing. The state has its own, older MCLs (14 ppt for PFOA and PFOS) that predate the federal rule, meaning some systems thought they were compliant and are not under the new standard.
2. Massachusetts: 439 systems, 80.1% detection rate
Massachusetts has the second-highest number of affected water systems nationally and an 80.1% detection rate, meaning roughly four out of five public water systems tested found PFAS. The state's Department of Environmental Protection estimates 181 systems will need treatment under the new 4 ppt limits. The highest recorded level is 142 ppt. Sources include Saint-Gobain and Chemours industrial sites.
3. Michigan: max 620 ppt, 58 systems exceeding MCL
Michigan's situation is defined by one number: 620 parts per trillion, the highest single-sample PFAS level recorded in any state in our dataset. That reading is from the Rockford area, downstream of a former 3M manufacturing plant where Scotchgard (a PFAS product) was produced for decades. The town of Parchment discovered its entire water system was contaminated in 2018; the state distributed bottled water to residents for months. Michigan now has MCLs for seven different PFAS compounds.
4. New Hampshire: 202 systems, 81.5% detection rate, max 185 ppt
New Hampshire matches New Jersey's 81.5% detection rate and has 68 systems exceeding the federal MCL. The primary sources are Pease Air Force Base, where PFAS-containing firefighting foam was used for decades, and the Saint-Gobain Performance Plastics plant in Merrimack, which released PFAS into the air and groundwater. The Merrimack area had PFAS levels in municipal water that exceeded 100 ppt before treatment was installed.
5. North Carolina: max 680 ppt, most widespread contamination in region
North Carolina has the highest single-sample PFAS reading outside Michigan: 680 parts per trillion, measured in systems near the Chemours Fayetteville Works plant on the Cape Fear River. Chemours manufactures GenX, a PFAS compound used as a replacement for the now-banned PFOA. The Cape Fear Public Utility Authority, which serves Wilmington and surrounding areas, has been dealing with GenX contamination for years and has installed treatment. The broader problem: GenX wasn't initially covered by regulatory limits, and by the time it was, it had been discharged for years.
States With Minimal Contamination
Three states have no documented above-MCL detections in UCMR 5 data: Arkansas (max 3 ppt, just below the 4 ppt MCL), Hawaii (max 3 ppt), and North Dakota (max 2 ppt). These states share characteristics: lower industrial footprints, fewer military bases with documented AFFF use, and less agricultural application of PFAS-containing biosolids.
What to Do If You're in a High-Contamination State
First, look up your specific water system, as state averages hide significant local variation. A home in inland New Jersey may have very different water than one near a former industrial site. Second, if your system tests above the MCL, a certified reverse osmosis system or activated carbon block filter (NSF/ANSI 58 certified) can remove a significant fraction of PFAS from drinking water. Third, if you're on a private well in any of the states above (especially near military bases or industrial sites), get your well tested. Wells are not covered by the UCMR 5 monitoring program.
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