Cities With the Highest PFAS Levels in Drinking Water
Ranked list of US public water systems with the highest recorded PFAS "forever chemical" levels in EPA nationwide monitoring. The highest readings are historical peaks (largely EPA UCMR3, 2013-2015 – the most recent round with systems above 4 ppt) and some systems have since added treatment. 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 on record? Commonwealth Utilities Corp. (Saipan), Northern Mariana Islands recorded the highest PFAS level at 7,000 ppt in EPA nationwide testing – a historical peak (largely EPA UCMR3, 2013-2015) that may since have been treated.
How do these rankings work? Rankings use the single maximum PFAS level recorded at each water system in EPA nationwide monitoring (largely UCMR3, 2013-2015). 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; Saint Paul Park (Minnesota): 1,700 ppt; Security WSD (Colorado): 1,300 ppt; Warminster Municipal Authority (Pennsylvania): 1,090 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; Saint Paul Park (Minnesota): 1,700 ppt; Security WSD (Colorado): 1,300 ppt; Warminster Municipal Authority (Pennsylvania): 1,090 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 recorded at each water system in EPA nationwide monitoring (largely UCMR3, 2013-2015 – the most recent round with systems above 4 ppt). Water systems are identified by their Public Water System ID (PWSID) and name as reported to the EPA. The list is sorted by the single highest recorded reading – not the average, which can mask dangerous peaks. These are historical peaks; some systems have since added treatment.
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 | 1386.49 | 7 |
| 2 | Artesian Water Company | Delaware | 1,800 | 147.51 | 30 |
| 3 | Saint Paul Park | Minnesota | 1,700 | 1225 | 4 |
| 4 | Security WSD | Colorado | 1,300 | 332.46 | 7 |
| 5 | Warminster Municipal Authority | Pennsylvania | 1,090 | 474.75 | 4 |
| 6 | Horsham Water & Sewer Authority | Pennsylvania | 1,000 | 411.06 | 5 |
| 7 | Oatman Water Company | Arizona | 730 | 515 | 2 |
| 8 | CITY OF SUGAR LAND | Texas | 672 | 293.15 | 10 |
| 9 | Warrington Township Water & Sewer Department | Pennsylvania | 666.66 | 342.95 | 3 |
| 10 | IOWA-AMERICAN WTR CO-CLINTON DISTRICT | Iowa | 647.9 | 647.15 | 4 |
| 11 | Issaquah Water System | Washington | 600 | 420.5 | 2 |
| 12 | CITY OF GONZALES | Texas | 597 | 597 | 1 |
| 13 | Newport | Minnesota | 550 | 370 | 8 |
| 14 | Suffolk County Water Authority | New York | 530 | 250.67 | 3 |
| 15 | NASHVILLE, TOWN OF | North Carolina | 490 | 247.71 | 3 |
| 16 | CROSS TIMBERS WSC | Texas | 441 | 441 | 1 |
| 17 | Oakdale | Minnesota | 439 | 123.69 | 14 |
| 18 | Hyannis Water System | Massachusetts | 430 | 205 | 4 |
| 19 | City of Tucson | Arizona | 420 | 238 | 2 |
| 20 | GU Waterworks Authority - Northern System | Guam | 410 | 100.87 | 20 |
| 21 | City of Cleveland Heights | Ohio | 400 | 400 | 1 |
| 22 | Woodbury | Minnesota | 386 | 243.8 | 47 |
| 23 | Emerald Coast Utilities Authority | Florida | 380 | 145.38 | 12 |
| 24 | Calhoun | Georgia | 370 | 157.09 | 11 |
| 25 | United Water PA | Pennsylvania | 363 | 286 | 2 |
| 26 | CITY OF CAMERON | Texas | 339 | 220.62 | 5 |
| 27 | Widefield WSD | Colorado | 330 | 103.5 | 27 |
| 28 | Rome | Georgia | 330 | 125.12 | 5 |
| 29 | Sanford Water District | Maine | 290 | 200 | 2 |
| 30 | PRESCOTT WATERWORKS | Wisconsin | 280 | 245 | 4 |
| 31 | EXPERIMENTAL | Puerto Rico | 260 | 129.8 | 5 |
| 32 | POTRERO ELEMENTARY SCHOOL | California | 250.2 | 114.36 | 22 |
| 33 | Hastings, MN | Minnesota | 240 | 124.3 | 16 |
| 34 | RUNNING SPRINGS WATER DISTRICT | California | 236.5 | 166 | 4 |
| 35 | COLLEGEVILLE TRAPPE JOINT PWD | Pennsylvania | 235 | 235 | 1 |
| 36 | IL American - Lincoln | Illinois | 233.2 | 128.22 | 10 |
| 37 | Cottage Grove | Minnesota | 220 | 151.67 | 12 |
| 38 | NEWTON FALLS CITY | Ohio | 220 | 137.5 | 2 |
| 39 | Liberty Water LPSCO | Arizona | 220 | 97.84 | 5 |
| 40 | Wright-Patterson AFB Area A/C | Ohio | 210 | 180 | 2 |
| 41 | Doylestown Twp. Muni. Authority | Pennsylvania | 206.05 | 146.48 | 2 |
| 42 | CITY OF ANGLETON | Texas | 205 | 109.28 | 9 |
| 43 | TELFORD BOROUGH AUTHORITY | Pennsylvania | 202.2 | 114.3 | 6 |
| 44 | SIENNA PLANTATION MUD 10 | Texas | 194 | 194 | 1 |
| 45 | MDWASA - MAIN SYSTEM | Florida | 190 | 97.22 | 10 |
| 46 | City of Fountain | Colorado | 190 | 77.1 | 12 |
| 47 | Bemidji | Minnesota | 187 | 160 | 2 |
| 48 | Freeport | Illinois | 180 | 119.5 | 2 |
| 49 | VAW Water System, Inc. | Alabama | 180 | 135 | 2 |
| 50 | CITY OF RICHWOOD | Texas | 180 | 134.63 | 3 |
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.