Is there PFAS in Atascadero Mutual Water CO water?
Yes. EPA's final UCMR 5 results show Atascadero Mutual Water CO averaged 21.6 ppt of PFOS at its worst sampling point, 5.4 times the EPA limit of 4 ppt.
Atascadero Mutual Water CO
Serves 30,618 people · 8 PFOA samples from 4 sampling points · Apr 2023 to Oct 2023
Average above an EPA limit
PFOA Perfluorooctanoic acid
7.9 ppt avg · max 8.4
PFOS Perfluorooctanesulfonic acid
21.6 ppt avg · max 22.3
PFHxS Perfluorohexanesulfonic acid
5.9 ppt avg · max 7.6
Hazard index GenX, PFBS, PFNA, PFHxS combined
0.6 avg · max 0.8
Also detected, no federal limit: PFBA, PFBS.
Atascadero Mutual Water CO is a public water system drawing on groundwater, based in Atascadero, California, serving about 30,618 people. Under EPA's Fifth Unregulated Contaminant Monitoring Rule it was tested for 29 PFAS and lithium 8 times across 4 sampling points between Apr 2023 and Oct 2023.
Every PFAS detected
Not detected: PFTrDA, 8:2 FTS, PFMPA, PFMBA, PFEESA, NFDHA, PFPeS, PFHpS, PFTA, NEtFOSAA, NMeFOSAA, 4:2 FTS, HFPO-DA, PFPeA, PFHpA, 6:2 FTS, PFNA, PFDA, ADONA, PFUnA, 9Cl-PF3ONS, PFDoA, PFHxA, 11Cl-PF3OUdS.
Lithium, tested in the same program: highest 20.7 ppb, detected in 6 of 8 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
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
93422
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 Atascadero Mutual Water CO water: EPA UCMR 5 results." Data: U.S. EPA Fifth Unregulated Contaminant Monitoring Rule, final release August 2026, PWSID CA4010002. https://wellandtap.com/pfas/california/atascadero-mutual-water-co/
About this data
Source: U.S. EPA, UCMR 5 occurrence data, final release August 2026 (PWSID CA4010002). Population: EPA SDWIS. Averages count results below the reporting level as zero, the same convention EPA uses for running annual averages. Full method.
