Is there PFAS in Western Mwd water?
Yes, at low levels. 3 PFAS were detected, all below EPA's 2024 limits.
Western Mwd
Serves 86,062 people · 12 PFOA samples from 3 sampling points · Mar 2023 to Jan 2024
PFAS found, below EPA limits
PFOA Perfluorooctanoic acid
not detected
PFOS Perfluorooctanesulfonic acid
not detected
PFHxS Perfluorohexanesulfonic acid
0.8 ppt avg · max 3.4
Hazard index GenX, PFBS, PFNA, PFHxS combined
0.1 avg · max 0.3
Also detected, no federal limit: PFPeA, PFBS.
Western Mwd is a public water system drawing on surface water, based in Riverside, California, serving about 86,062 people, including Encino, Burbank, Ontario, Diamond Bar, Riverside, March Air Reserve Base. Under EPA's Fifth Unregulated Contaminant Monitoring Rule it was tested for 29 PFAS and lithium 12 times across 3 sampling points between Mar 2023 and Jan 2024.
Every PFAS detected
Not detected: PFOA, 6:2 FTS, PFBA, HFPO-DA, ADONA, 9Cl-PF3ONS, 11Cl-PF3OUdS, PFUnA, PFHxA, PFDA, 4:2 FTS, PFNA, PFDoA, PFMBA, NMeFOSAA, PFOS, PFHpS, PFPeS, PFEESA, 8:2 FTS, PFMPA, PFHpA, PFTA, PFTrDA, NEtFOSAA, NFDHA.
Lithium, tested in the same program: highest 16 ppb, detected in 1 of 12 samples. EPA's health-based screening level is 10 ppb.
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
Levels here are under EPA's limits, so no treatment is required. If you want them lower anyway, a certified reverse osmosis system under the sink handles drinking water, and a whole-house carbon filter also takes out the chlorine or chloramine your utility adds.
Other systems in California
All 707 tested systems in California
ZIP codes served
91436 91504 91761 91765 92501 92503 92504 92505 92506 92507 92508 92509 92513 92517 92518 92532 92551 92553 92557 92570 92660 92870 92879 92881 92883
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 Western Mwd water: EPA UCMR 5 results." Data: U.S. EPA Fifth Unregulated Contaminant Monitoring Rule, final release August 2026, PWSID CA3310049. https://wellandtap.com/pfas/california/western-mwd/
About this data
Source: U.S. EPA, UCMR 5 occurrence data, final release August 2026 (PWSID CA3310049). Population: EPA SDWIS. Averages count results below the reporting level as zero, the same convention EPA uses for running annual averages. Full method.
