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The 10 U.S. water systems serving 10,000 or more people with the highest PFOA or PFOS averages in EPA's latest PFAS data (UCMR 5, file dated Oct 15, 2026)

EPA UCMR 5 file dated Oct 15, 2026 · population from EPA SDWIS, Oct 14, 2026 · checked Nov 15, 2026

Ranked by each system's higher average of PFOA or PFOS in EPA's UCMR 5 testing. Monitoring results, not violations.

No. 1
Montebello Land & Water CO.
serving Montebello, CA
43.5ppt PFOS
6 samples, 2023 to 2024

2 of these 10 serve communities in Miami-Dade County.

A clear glass of water on a sunlit counter.

Only utilities with at least 4 samples are ranked.

Nationwide, 656 of 9,947 water systems with PFOA or PFOS results in EPA's UCMR 5 data averaged above 4.0 ppt.

In Florida, 101 of 393 water systems with PFOA or PFOS results in EPA's UCMR 5 data averaged above 4.0 ppt.

Systems serving 10,000 or more people (EPA SDWIS population served, Oct 14, 2026)

Systems serving 10,000 or more people (EPA SDWIS population served, Oct 14, 2026)
RankWater systemPFOA averagePFOS averagePeople served (EPA SDWIS, Oct 14, 2026)Sample yearsEPA's 2024 level (4.0 ppt)
1Montebello Land & Water CO.serving Montebello, CAPWSID CA1910091State records (2023) show an ion exchange treatment project planned for its wells. Source9.3 ppt6 samples43.5 ppt6 samples26,5542023 to 2024Above 4.0 ppt
2Emmaus Borough Public Waterserving Emmaus, PAPWSID PA339003211.0 ppt8 samples35.5 ppt8 samples14,0002024 to 2025Above 4.0 ppt
3MDWASA/Rex Utilitiesserving Miami, FLPWSID FL41312025.2 ppt10 samples29.5 ppt10 samples45,2002025Above 4.0 ppt
4North Miami, City ofserving North Miami, FLPWSID FL41309776.0 ppt4 samples28.0 ppt4 samples89,3492023 to 2024Above 4.0 ppt
5Downey - City, Water Dept.serving Downey, CAPWSID CA191003411.1 ppt10 samples26.2 ppt10 samples110,5562025Above 4.0 ppt
6Fort Campbell Water System(Montgomery County, TN in EPA records)PWSID TN00008205.8 ppt4 samples24.8 ppt4 samples43,2702023 to 2024Above 4.0 ppt
7Gadsden, the WWSB of the City ofserving Gadsden, ALPWSID AL0000577News reports say Gadsden is building a reverse osmosis plant, expected in 2027. SourceGadsden has used carbon (GAC) treatment since 2018, so these results were measured with it in place. Source23.5 ppt4 samples22.7 ppt4 samples44,6372023 to 2024Above 4.0 ppt
8Tarpon Springs Water System(Tarpon Springs, FL in EPA records)PWSID FL6521784Tarpon Springs opened a reverse osmosis plant in 2015 (Treatment Plant Operator). Source6.5 ppt6 samples23.4 ppt6 samples28,8752023Above 4.0 ppt
9Irondale Water Systemserving Irondale, ALPWSID AL00007512.6 ppt4 samples23.0 ppt4 samples10,0982023Above 4.0 ppt
10Greensboro, City ofserving Greensboro, NCPWSID NC0241010Greensboro's city council approved $260 million for PFAS treatment in October 2026 (WFDD). SourceGreensboro has used powdered activated carbon at its Mitchell plant since 2018. Source1.8 ppt8 samples22.7 ppt8 samples319,5882023 to 2024Above 4.0 ppt

The 10 U.S. water systems with the highest PFOA or PFOS averages, all system sizes (UCMR 5, file dated Oct 15, 2026)

The 10 U.S. water systems with the highest PFOA or PFOS averages, all system sizes (UCMR 5, file dated Oct 15, 2026)
RankWater systemPFOA averagePFOS averagePeople served (EPA SDWIS, Oct 14, 2026)Sample yearsEPA's 2024 level (4.0 ppt)
1Yeshiva Farm Settlement(Town of New Castle, NY in EPA records)PWSID NY590315025.0 ppt4 samples94.5 ppt4 samples3002023Above 4.0 ppt
2Nashville, Town of(Nashville, NC in EPA records)PWSID NC04640203.0 ppt10 samples72.4 ppt10 samples5,9002024 to 2025Above 4.0 ppt
3Orangewood Water System(Holiday, FL in EPA records)PWSID FL651131117.6 ppt10 samples64.3 ppt10 samples6,4642023Above 4.0 ppt
4Montebello Land & Water CO.serving Montebello, CAPWSID CA1910091State records (2023) show an ion exchange treatment project planned for its wells. Source9.3 ppt6 samples43.5 ppt6 samples26,5542023 to 2024Above 4.0 ppt
5Lake Panasoffkee Water Assn 2WPS(Lake Panasoffkee, FL in EPA records)PWSID FL66009906.2 ppt4 samples36.8 ppt4 samples4,6422023Above 4.0 ppt
6Emmaus Borough Public Waterserving Emmaus, PAPWSID PA339003211.0 ppt8 samples35.5 ppt8 samples14,0002024 to 2025Above 4.0 ppt
7MDWASA/Rex Utilitiesserving Miami, FLPWSID FL41312025.2 ppt10 samples29.5 ppt10 samples45,2002025Above 4.0 ppt
8North Miami, City ofserving North Miami, FLPWSID FL41309776.0 ppt4 samples28.0 ppt4 samples89,3492023 to 2024Above 4.0 ppt
9Collegeville Trappe Joint PWD(Montgomery County, PA in EPA records)PWSID PA1460022Collegeville's council approved an interconnection with North Penn Water Authority in April 2026. Source27.9 ppt13 samples9.7 ppt13 samples8,4702023Above 4.0 ppt
10Downey - City, Water Dept.serving Downey, CAPWSID CA191003411.1 ppt10 samples26.2 ppt10 samples110,5562025Above 4.0 ppt

Both tables: ranked on the higher exact average of PFOA or PFOS, with non-detects counted as zero. Only systems with at least 4 samples for that compound are ranked. Sample years are on each row.

Systems marked "Above 4.0 ppt" averaged above 4.0 ppt, the level EPA set in 2024, not yet enforceable (water systems must meet it by April 2029; EPA has proposed allowing until 2031). These are monitoring results, not violations.

Not a test of your tap. Download the data (CSV)

Systems serving 10,000 or more people

Bar chart of the 10 systems' highest PFOA or PFOS averages: Montebello Land & Water CO. 43.5; Emmaus Borough Public Water 35.5; MDWASA/Rex Utilities 29.5; North Miami, City of 28.0; Downey - City, Water Dept. 26.2; Fort Campbell Water System 24.8; Gadsden, the WWSB of the City of 23.5; Tarpon Springs Water System 23.4; Irondale Water System 23.0; Greensboro, City of 22.7 ppt.1. Montebello Land & Water CO.43.5 PFOS2. Emmaus Borough Public Water35.5 PFOS3. MDWASA/Rex Utilities29.5 PFOS4. North Miami, City of28.0 PFOS5. Downey - City, Water Dept.26.2 PFOS6. Fort Campbell Water System24.8 PFOS7. Gadsden, the WWSB of the City of23.5 PFOA8. Tarpon Springs Water System23.4 PFOS9. Irondale Water System23.0 PFOS10. Greensboro, City of22.7 PFOSEPA 2024 level: 4.0 ppt
Each bar is the system's higher exact average (ppt). The line marks 4.0 ppt, the level EPA set in 2024, not yet enforceable. Source: EPA UCMR 5, file dated October 15, 2026; ScoreYourWater analysis.

Highest PFOA or PFOS average, all system sizes

Bar chart of the 10 systems' highest PFOA or PFOS averages: Yeshiva Farm Settlement 94.5; Nashville, Town of 72.4; Orangewood Water System 64.3; Montebello Land & Water CO. 43.5; Lake Panasoffkee Water Assn 2WPS 36.8; Emmaus Borough Public Water 35.5; MDWASA/Rex Utilities 29.5; North Miami, City of 28.0; Collegeville Trappe Joint PWD 27.9; Downey - City, Water Dept. 26.2 ppt.1. Yeshiva Farm Settlement94.5 PFOS2. Nashville, Town of72.4 PFOS3. Orangewood Water System64.3 PFOS4. Montebello Land & Water CO.43.5 PFOS5. Lake Panasoffkee Water Assn 2WPS36.8 PFOS6. Emmaus Borough Public Water35.5 PFOS7. MDWASA/Rex Utilities29.5 PFOS8. North Miami, City of28.0 PFOS9. Collegeville Trappe Joint PWD27.9 PFOA10. Downey - City, Water Dept.26.2 PFOSEPA 2024 level: 4.0 ppt
Each bar is the system's higher exact average (ppt). The line marks 4.0 ppt, the level EPA set in 2024, not yet enforceable. Source: EPA UCMR 5, file dated October 15, 2026; ScoreYourWater analysis.

States with the most water systems averaging above 4.0 ppt

Bar chart of states by number of water systems above 4.0 ppt: FL 101; NJ 73; NC 60; CA 49; AL 45; PA 45; SC 45; OH 34; MA 29; TX 19.FL101 of 393NJ73 of 244NC60 of 283CA49 of 676AL45 of 306PA45 of 360SC45 of 163OH34 of 331MA29 of 261TX19 of 1,129
Systems whose PFOA or PFOS average was above 4.0 ppt, by state, out of systems with PFOA or PFOS results. Source: EPA UCMR 5, file dated October 15, 2026; ScoreYourWater analysis. Tribal systems are not assigned to a state.

How we did this

  • Each average is the exact mean of all of the system's UCMR 5 results for that compound, with non-detects counted as zero. Systems are ranked on the higher of the PFOA and PFOS averages, unrounded; the page shows one decimal.
  • Only utilities with at least 4 samples are ranked. Sample years are shown on each row.
  • EPA UCMR 5 file dated October 15, 2026 (samples through June 17, 2026). 7,942 systems qualified.
  • The lead list uses the same method, limited to systems serving 10,000 or more people by EPA SDWIS population served (Oct 14, 2026).
  • Both values, PFOA and PFOS, are shown for each system. They are never blended into one PFAS average.

These are monitoring results, not violations. Not a test of your tap.

ScoreYourWater also sells water treatment systems.

Sources

  • EPA UCMR 5 occurrence data
  • EPA ECHO Safe Drinking Water Act data (system names, population served)
  • EPA PFAS drinking water rule (2024)

Utilities: see something wrong? Send a correction

Data as of October 14, 2026. The list is updated monthly. Corrections are noted in each monthly update.

More rankings

  • The Florida top 10
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