Is there PFAS in Cwsc Los Altos Suburban water?
Yes, at low levels. 1 PFAS was detected, all below EPA's 2024 limits.
Cwsc Los Altos Suburban
Serves 69,973 people · 36 PFOA samples from 16 sampling points · Jun 2023 to Mar 2025
PFAS found, below EPA limits
PFOA Perfluorooctanoic acid
not detected
PFOS Perfluorooctanesulfonic acid
not detected
PFHxS Perfluorohexanesulfonic acid
1.8 ppt avg · max 3.5
Hazard index GenX, PFBS, PFNA, PFHxS combined
0.2 avg · max 0.3
Cwsc Los Altos Suburban is a public water system drawing on surface water, based in San Jose, California, serving about 69,973 people, including Los Altos, Mountain View, Sunnyvale, Palo Alto, Cupertino, Santa Clara. Under EPA's Fifth Unregulated Contaminant Monitoring Rule it was tested for 29 PFAS and lithium 36 times across 16 sampling points between Jun 2023 and Mar 2025.
Every PFAS detected
Not detected: NFDHA, PFPeS, PFEESA, PFMBA, PFPeA, PFMPA, 8:2 FTS, 4:2 FTS, 6:2 FTS, PFBA, HFPO-DA, ADONA, 9Cl-PF3ONS, 11Cl-PF3OUdS, PFBS, PFHpS, PFTrDA, PFUnA, NMeFOSAA, PFTA, PFHpA, PFNA, PFOS, PFOA, PFDA, PFDoA, PFHxA, NEtFOSAA.
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
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
94022 94024 94040 94041 94086 94087 94306 95014 95051
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 Cwsc Los Altos Suburban water: EPA UCMR 5 results." Data: U.S. EPA Fifth Unregulated Contaminant Monitoring Rule, final release August 2026, PWSID CA4310001. https://wellandtap.com/pfas/california/cwsc-los-altos-suburban/
About this data
Source: U.S. EPA, UCMR 5 occurrence data, final release August 2026 (PWSID CA4310001). Population: EPA SDWIS. Averages count results below the reporting level as zero, the same convention EPA uses for running annual averages. Full method.
