Is there PFAS in Gwa Northern Water System water?
Yes. EPA's final UCMR 5 results show Gwa Northern Water System averaged 67.5 ppt of PFOS at its worst sampling point, 16.9 times the EPA limit of 4 ppt.
Gwa Northern Water System
Serves 139,207 people · 121 PFOA samples from 61 sampling points · Sep 2023 to Dec 2025
Average above an EPA limit
PFOA Perfluorooctanoic acid
13.4 ppt avg · max 18.3
PFOS Perfluorooctanesulfonic acid
67.5 ppt avg · max 135
PFHxS Perfluorohexanesulfonic acid
40.0 ppt avg · max 80.0
Hazard index GenX, PFBS, PFNA, PFHxS combined
4.0 avg · max 8.0
Also detected, no federal limit: 6:2 FTS, PFPeA, PFHxA, PFBS, PFHpA, PFBA, PFPeS, 8:2 FTS.
Gwa Northern Water System is a public water system drawing on groundwater, based in Mangilao, Guam, serving about 139,207 people. Under EPA's Fifth Unregulated Contaminant Monitoring Rule it was tested for 29 PFAS and lithium 121 times across 61 sampling points between Sep 2023 and Dec 2025.
Every PFAS detected
Not detected: PFDoA, PFNA, PFDA, PFUnA, 11Cl-PF3OUdS, 9Cl-PF3ONS, ADONA, NEtFOSAA, PFTA, PFTrDA, 4:2 FTS, NMeFOSAA, HFPO-DA, PFHpS, NFDHA, PFEESA, PFMBA, PFMPA.
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 Guam
All 5 tested systems in Guam
ZIP codes served
96910 96913 96915 96929
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 Gwa Northern Water System water: EPA UCMR 5 results." Data: U.S. EPA Fifth Unregulated Contaminant Monitoring Rule, final release August 2026, PWSID GU0000006. https://wellandtap.com/pfas/guam/gwa-northern-water-system/
About this data
Source: U.S. EPA, UCMR 5 occurrence data, final release August 2026 (PWSID GU0000006). Population: EPA SDWIS. Averages count results below the reporting level as zero, the same convention EPA uses for running annual averages. Full method.
