The Most PFAS-Contaminated Water Systems in America
US public water systems with the highest recorded PFAS "forever chemical" levels, based on EPA UCMR3 (2013-2015) – the most recent nationwide monitoring round in which systems exceeded the EPA's 4 ppt threshold for PFOA and PFOS. These are historical peak readings; some systems have since added treatment or taken affected sources offline. Often searched as the worst US cities for water quality, this ranking is by water system (utility), the unit the EPA actually tests. Find out if yours ranks among the worst on record.
Quick Answers
Which US water system has the worst PFAS contamination on record? Commonwealth Utilities Corp. (Saipan) in MP recorded the highest PFAS level in EPA nationwide testing at 7,000 ppt - roughly 1750x the EPA's 4 ppt limit. This is a historical peak (EPA UCMR3, 2013-2015); the affected source may since have been treated or taken offline.
How is "worst" defined here? By the single highest PFAS reading ever recorded at each public water system in EPA nationwide monitoring. 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 recorded at each water system in EPA UCMR3 (2013-2015), the most recent nationwide monitoring round with systems above the 4 ppt threshold. (UCMR5 (2023-2025) detections in our dataset fall below that threshold.) Systems are identified by Public Water System ID (PWSID) and the name reported to the EPA, then sorted by their single highest reading, which shows each system's "EPA multiplier" - how many times over the 2024 federal limit its peak sits. Lithium, a co-analyte the EPA reports alongside PFAS at much higher concentrations, is excluded so the ranking reflects PFAS only.
Data vintage: EPA UCMR3 (2013-2015). Because these are historical peaks, some systems have since installed treatment. Source: EPA Unregulated Contaminant Monitoring Rule.
Water Systems Ranked by Peak 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 | Rome | GA | 330 | 82.5x | Extreme |
| 19 | Widefield WSD | CO | 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 | VAW Water System, Inc. | AL | 180 | 45x | Extreme |
| 27 | City of Stuart Water Plant | FL | 180 | 45x | Extreme |
| 28 | Freeport | IL | 180 | 45x | Extreme |
| 29 | City of Newburgh | NY | 170 | 42.5x | Extreme |
| 30 | Westfield Water Department | MA | 170 | 42.5x | Extreme |
| 31 | City of Zephyrhills | FL | 160 | 40x | Extreme |
| 32 | CA American Water Co. - Suburban | CA | 156 | 39x | Extreme |
| 33 | Northeast Alabama Water System | AL | 150 | 37.5x | Extreme |
| 34 | City of Tempe | AZ | 150 | 37.5x | Extreme |
| 35 | La Crosse Waterworks | WI | 140 | 35x | Extreme |
| 36 | New Windsor Consolidated Water District | NY | 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.