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Is there PFAS in Ontario Municipal Utilities Company water?

Yes. EPA's final UCMR 5 results show Ontario Municipal Utilities Company averaged 15.0 ppt of PFOA at its worst sampling point, 3.8 times the EPA limit of 4 ppt.

Ontario Municipal Utilities Company Serves 185,010 people · 36 PFOA samples from 17 sampling points · Feb 2023 to Feb 2024 Average above an EPA limit
PFOA Perfluorooctanoic acid 15.0 ppt avg · max 30.0
EPA 4
PFOS Perfluorooctanesulfonic acid 2.6 ppt avg · max 5.2
EPA 4
PFHxS Perfluorohexanesulfonic acid 2.1 ppt avg · max 4.2
EPA 10
Hazard index GenX, PFBS, PFNA, PFHxS combined 0.2 avg · max 0.4
EPA 1

Also detected, no federal limit: PFHxA, PFPeA, PFBA.

Averages are for the worst sampling point, with non-detects counted as zero. Source: EPA UCMR 5.

Ontario Municipal Utilities Company is a public water system drawing on surface water, based in Ontario, California, serving about 185,010 people. Under EPA's Fifth Unregulated Contaminant Monitoring Rule it was tested for 29 PFAS and lithium 36 times across 17 sampling points between Feb 2023 and Feb 2024.

Every PFAS detected

PFAS Detected Highest Worst point avg EPA limit
PFOA
Perfluorooctanoic acid		 1 of 36 30.0 ppt 15.0 ppt 4 ppt
PFHxA
Perfluorohexanoic acid		 1 of 36 7.1 ppt 3.6 ppt none
PFPeA
Perfluoropentanoic acid		 2 of 36 6.7 ppt 5.8 ppt none
PFBA
Perfluorobutanoic acid		 2 of 36 6.4 ppt 3.2 ppt none
PFOS
Perfluorooctanesulfonic acid		 1 of 36 5.2 ppt 2.6 ppt 4 ppt
PFHxS
Perfluorohexanesulfonic acid		 1 of 36 4.2 ppt 2.1 ppt 10 ppt

Not detected: PFBS, PFUnA, PFDoA, PFDA, 11Cl-PF3OUdS, PFHpA, NMeFOSAA, NEtFOSAA, PFTrDA, PFTA, PFNA, PFHpS, 9Cl-PF3ONS, NFDHA, PFMBA, PFPeS, PFMPA, 8:2 FTS, 4:2 FTS, 6:2 FTS, HFPO-DA, ADONA, PFEESA.

Lithium, tested in the same program: not detected.

What the EPA limits mean here

In April 2024 EPA set enforceable limits of 4 ppt for PFOA and PFOS, 10 ppt each for PFHxS, PFNA and GenX, and a hazard index of 1 for mixtures. Utilities were given until 2029 to comply. In May 2026 EPA proposed keeping only the PFOA and PFOS limits and moving that deadline to 2031. Until that proposal is final, the 2024 limits stand.

Compliance is judged on a running annual average at each entry point, so we show the average at this system's worst sampling point next to its single highest result. UCMR 5 results do not by themselves put a utility in or out of compliance.

What you can do at home

Two routes work for PFAS. For drinking and cooking water only, a reverse osmosis system certified to NSF/ANSI 58 with a PFOA/PFOS reduction claim is the cheapest proven option. To treat every tap and shower, a whole-house carbon system with enough contact time works, but check that the maker has PFAS test data, not just a marketing claim. See the best filters for PFAS and how PFAS removal works.

Other systems in California

All 707 tested systems in California

ZIP codes served

91761 91762 91764

As reported by the utility to EPA. Neighbouring ZIPs are often split between systems; your water bill names yours.

Cite this page

Well & Tap. "PFAS in Ontario Municipal Utilities Company water: EPA UCMR 5 results." Data: U.S. EPA Fifth Unregulated Contaminant Monitoring Rule, final release August 2026, PWSID CA3610034. https://wellandtap.com/pfas/california/ontario-municipal-utilities-company/

About this data

Source: U.S. EPA, UCMR 5 occurrence data, final release August 2026 (PWSID CA3610034). Population: EPA SDWIS. Averages count results below the reporting level as zero, the same convention EPA uses for running annual averages. Full method.