Cities With the Highest PFAS Levels in Drinking Water
Ranked list of US public water systems with the highest detected PFAS "forever chemical" levels, based on EPA UCMR5 monitoring data. Systems exceeding the EPA's 4 ppt limit for PFOA and PFOS are flagged for residents to consider filtration and, potentially, legal action.
Quick Answers
Which US city has the worst PFAS water contamination? Commonwealth Utilities Corp. (Saipan), Northern Mariana Islands currently shows the highest recorded PFAS level at 7,000 ppt in EPA UCMR5 testing.
How do these rankings work? Rankings use the single maximum detected PFAS level at each water system during EPA UCMR5 testing (2023-2025). We use the peak rather than the average because even one reading above 4 ppt triggers EPA compliance action under the 2024 PFAS Rule.
What are the top 5 most contaminated water systems? Commonwealth Utilities Corp. (Saipan) (Northern Mariana Islands): 7,000 ppt; Artesian Water Company (Delaware): 1,800 ppt; Security WSD (Colorado): 1,300 ppt; Warminster Municipal Authority (Pennsylvania): 1,090 ppt; Horsham Water & Sewer Authority (Pennsylvania): 1,000 ppt. Treatment is required under federal law for any system exceeding 4 ppt for PFOA or PFOS.
What should I do if my city is on this list? Install a certified reverse osmosis system (removes 90%+ of PFAS) or an NSF-53 certified pitcher for interim protection. Check our filter guide, and look up your specific utility's latest test results.
Top 5 Most Contaminated Water Systems
Commonwealth Utilities Corp. (Saipan) (Northern Mariana Islands): 7,000 ppt; Artesian Water Company (Delaware): 1,800 ppt; Security WSD (Colorado): 1,300 ppt; Warminster Municipal Authority (Pennsylvania): 1,090 ppt; Horsham Water & Sewer Authority (Pennsylvania): 1,000 ppt. These readings reflect the maximum detected level at each system during EPA testing. Even a single exceedance above 4 ppt requires treatment under the 2024 federal rule.
How This Ranking Is Calculated
Rankings are based on the maximum PFAS level detected at each water system during UCMR5 testing (2023-2025). Water systems are identified by their Public Water System ID (PWSID) and name as reported to the EPA. The list includes the top 50 systems sorted by the single highest reading – not the average, which can mask dangerous peaks.
Top 50 Water Systems by PFAS Level
| Rank | Water System | State | Max PPT | Avg PPT | Samples |
|---|---|---|---|---|---|
| 1 | Commonwealth Utilities Corp. (Saipan) | Northern Mariana Islands | 7,000 | 1890 | 5 |
| 2 | Artesian Water Company | Delaware | 1,800 | 873.33 | 3 |
| 3 | Security WSD | Colorado | 1,300 | 680 | 3 |
| 4 | Warminster Municipal Authority | Pennsylvania | 1,090 | 609.33 | 3 |
| 5 | Horsham Water & Sewer Authority | Pennsylvania | 1,000 | 626.67 | 3 |
| 6 | WATERPRO INC | Utah | 960 | 694.75 | 4 |
| 7 | CREEKSIDE VILLAGE MHP | New York | 921 | 921 | 1 |
| 8 | ARIZONA WATER CO - APACHE JUNCTION | Arizona | 796 | 733 | 8 |
| 9 | Oatman Water Company | Arizona | 730 | 515 | 2 |
| 10 | AQUA PA WATER CO HONESDALE | Pennsylvania | 702 | 469 | 8 |
| 11 | Warrington Township Water & Sewer Department | Pennsylvania | 666.66 | 455.24 | 2 |
| 12 | PHOENIX INTERNATIONAL RACEWAY | Arizona | 620 | 565.5 | 4 |
| 13 | Issaquah Water System | Washington | 600 | 420.5 | 2 |
| 14 | BERMUDA WATER COMPANY INC | Arizona | 580 | 277 | 20 |
| 15 | SANTA ANA WESTSIDE | 06 | 540 | 450 | 6 |
| 16 | BERNALILLO WATER SYSTEM | New Mexico | 537 | 411.75 | 4 |
| 17 | Suffolk County Water Authority | New York | 530 | 335 | 2 |
| 18 | MESA CITY OF | Arizona | 525 | 200.93 | 58 |
| 19 | INDIANOLA WATER SUPPLY | Iowa | 480 | 440 | 4 |
| 20 | CAL AM - OAKHURST | California | 474 | 340.67 | 6 |
| 21 | CITY OF BUCKEYE - VALENCIA TOWN DIVISION | Arizona | 468 | 446 | 4 |
| 22 | VERMILLION | South Dakota | 440 | 435 | 2 |
| 23 | Oakdale | Minnesota | 439 | 388.5 | 2 |
| 24 | Hyannis Water System | Massachusetts | 430 | 350 | 2 |
| 25 | City of Tucson | Arizona | 420 | 420 | 1 |
| 26 | WAPELLO RURAL WATER ASSOC. | Iowa | 420 | 375 | 4 |
| 27 | GU Waterworks Authority - Northern System | Guam | 410 | 275 | 2 |
| 28 | CITY OF WOODWAY | Texas | 403 | 403 | 1 |
| 29 | City of Cleveland Heights | Ohio | 400 | 400 | 1 |
| 30 | RIO RANCHO WATER & WW SERVICES | New Mexico | 393 | 292.4 | 5 |
| 31 | CORALVILLE MUNI WATER SYSTEM | Iowa | 390 | 285 | 4 |
| 32 | PIMA UTILITIES | Arizona | 381 | 316.33 | 6 |
| 33 | WEST DES MOINES WATER WORKS | Iowa | 380 | 370 | 4 |
| 34 | Emerald Coast Utilities Authority | Florida | 380 | 280 | 2 |
| 35 | MOUNT PLEASANT MUNICIPAL UTILITIES | Iowa | 370 | 262.5 | 8 |
| 36 | Calhoun | Georgia | 370 | 370 | 1 |
| 37 | United Water PA | Pennsylvania | 363 | 286 | 2 |
| 38 | ARIZONA WATER CO - PINAL VALLEY | Arizona | 353 | 265.93 | 30 |
| 39 | LAGUNA VALLEY | 06 | 343 | 328.5 | 8 |
| 40 | GOODYEAR WATER DEPARTMENT | Arizona | 335 | 226.67 | 6 |
| 41 | LOWER RIO GRANDE PWWA SOUTH VALLEY | New Mexico | 335 | 219.14 | 7 |
| 42 | ANTHONY W&SD | New Mexico | 335 | 281.5 | 2 |
| 43 | WOODRIDGE VILLAGE | New York | 335 | 250.75 | 4 |
| 44 | Widefield WSD | Colorado | 330 | 270 | 2 |
| 45 | Rome | Georgia | 330 | 330 | 1 |
| 46 | TRI COUNTY SUD | Texas | 325 | 231.75 | 4 |
| 47 | PA AMER WATER CO LAKE SCRANTON | Pennsylvania | 324 | 312.5 | 2 |
| 48 | FLORENCE WATER COMPANY | Arizona | 320 | 218.2 | 10 |
| 49 | PATTERSON VALLEY WC | Colorado | 309 | 300 | 4 |
| 50 | GLOBE CITY OF | Arizona | 308 | 301 | 4 |
What This Data Means for Residents
Water systems on this list have detected PFAS levels that significantly exceed EPA health advisory limits. Residents served by these systems should: (1) check their specific ZIP code at knowyourexposure.com, (2) consider an NSF/ANSI 58 certified reverse osmosis filter, and (3) if eligible, explore the PFAS lawsuit process. Major utilities exceeding the 4 ppt limit face federal compliance deadlines under the 2024 EPA PFAS rule.