Worst PFAS Contamination Cities in America
The 100 US public water systems with the highest detected PFAS "forever chemical" levels, based on EPA UCMR5 monitoring data (2023-2025). Every system listed exceeds the EPA's 4 ppt enforceable limit for PFOA and PFOS. Find out if your water system ranks among the worst.
Quick Answers
Which US water system has the worst PFAS contamination? Commonwealth Utilities Corp. (Saipan) in MP currently records the highest PFAS level at 7,000 ppt - roughly 1750x the EPA's 4 ppt limit.
How is "worst" defined here? By the single highest PFAS reading detected at each public water system during EPA UCMR5 testing. We rank on the peak reading rather than the average because even one result above 4 ppt triggers federal compliance action under the 2024 EPA PFAS Rule.
What are the 5 most contaminated systems? Commonwealth Utilities Corp. (Saipan) (MP): 7,000 ppt (1750x the EPA limit); Artesian Water Company (DE): 1,800 ppt (450x the EPA limit); Security WSD (CO): 1,300 ppt (325x the EPA limit); Warminster Municipal Authority (PA): 1,090 ppt (272.5x the EPA limit); Horsham Water & Sewer Authority (PA): 1,000 ppt (250x the EPA limit).
My city is on this list - what should I do? Install an NSF/ANSI 58 certified reverse osmosis system (removes 90%+ of PFAS) or an NSF-53 certified filter for interim protection. See our PFAS filter guide, then look up your specific utility's full results at knowyourexposure.com.
How This Ranking Is Calculated
Rankings use the maximum PFAS level detected at each water system during UCMR5 testing (2023-2025). Systems are identified by Public Water System ID (PWSID) and the name reported to the EPA, then sorted by their single highest reading. The list is limited to systems exceeding the 4 ppt EPA limit and shows each system's "EPA multiplier" - how many times over the federal limit its peak reading sits.
The 100 Worst Water Systems by PFAS Level
| Rank | Water System | State | Highest PFAS (ppt) | vs EPA Limit | Risk Level |
|---|---|---|---|---|---|
| 1 | Commonwealth Utilities Corp. (Saipan) | MP | 7,000 | 1750x | Extreme |
| 2 | Artesian Water Company | DE | 1,800 | 450x | Extreme |
| 3 | Security WSD | CO | 1,300 | 325x | Extreme |
| 4 | Warminster Municipal Authority | PA | 1,090 | 272.5x | Extreme |
| 5 | Horsham Water & Sewer Authority | PA | 1,000 | 250x | Extreme |
| 6 | Oatman Water Company | AZ | 730 | 182.5x | Extreme |
| 7 | Warrington Township Water & Sewer Department | PA | 666.66 | 166.7x | Extreme |
| 8 | Issaquah Water System | WA | 600 | 150x | Extreme |
| 9 | Suffolk County Water Authority | NY | 530 | 132.5x | Extreme |
| 10 | Oakdale | MN | 439 | 109.8x | Extreme |
| 11 | Hyannis Water System | MA | 430 | 107.5x | Extreme |
| 12 | City of Tucson | AZ | 420 | 105x | Extreme |
| 13 | GU Waterworks Authority - Northern System | GU | 410 | 102.5x | Extreme |
| 14 | City of Cleveland Heights | OH | 400 | 100x | Extreme |
| 15 | Emerald Coast Utilities Authority | FL | 380 | 95x | Extreme |
| 16 | Calhoun | GA | 370 | 92.5x | Extreme |
| 17 | United Water PA | PA | 363 | 90.8x | Extreme |
| 18 | Widefield WSD | CO | 330 | 82.5x | Extreme |
| 19 | Rome | GA | 330 | 82.5x | Extreme |
| 20 | Sanford Water District | ME | 290 | 72.5x | Extreme |
| 21 | Liberty Water LPSCO | AZ | 220 | 55x | Extreme |
| 22 | Wright-Patterson AFB Area A/C | OH | 210 | 52.5x | Extreme |
| 23 | Doylestown Twp. Muni. Authority | PA | 206.05 | 51.5x | Extreme |
| 24 | City of Fountain | CO | 190 | 47.5x | Extreme |
| 25 | Bemidji | MN | 187 | 46.8x | Extreme |
| 26 | City of Stuart Water Plant | FL | 180 | 45x | Extreme |
| 27 | Freeport | IL | 180 | 45x | Extreme |
| 28 | VAW Water System, Inc. | AL | 180 | 45x | Extreme |
| 29 | Westfield Water Department | MA | 170 | 42.5x | Extreme |
| 30 | City of Newburgh | NY | 170 | 42.5x | Extreme |
| 31 | City of Zephyrhills | FL | 160 | 40x | Extreme |
| 32 | CA American Water Co. - Suburban | CA | 156 | 39x | Extreme |
| 33 | City of Tempe | AZ | 150 | 37.5x | Extreme |
| 34 | Northeast Alabama Water System | AL | 150 | 37.5x | Extreme |
| 35 | New Windsor Consolidated Water District | NY | 140 | 35x | Extreme |
| 36 | La Crosse Waterworks | WI | 140 | 35x | Extreme |
| 37 | West Morgan - East Lawrence Water Authority | AL | 130 | 32.5x | Extreme |
| 38 | Vienna | WV | 129 | 32.3x | Extreme |
What This Data Means for Residents
Systems on this list have detected PFAS far above EPA health limits. If you are served by one, you should: (1) check your specific ZIP code at knowyourexposure.com, (2) install a certified reverse osmosis or NSF-53 filter, and (3) if eligible, review the PFAS lawsuit process. Utilities exceeding 4 ppt face federal treatment deadlines under the 2024 EPA PFAS Rule.