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Gwa Northern Water System water quality report, rewritten

Serves
139,207
Connections
39,541
Water source
Groundwater
Based in
Talofofo, GU
County
Guam
Owner
State government
The 4 ZIP codes it serves

96910, 96913, 96915, 96929

PWSID GU0000006 · EPA data

Read this first

  • Copper (above the health goal) In the latest period, 9 in 10 homes sampled were at or below 170 ppm, above the 1.3 ppm action level.
  • PFOS (above the health goal) was found in 37 of 121 samples, highest 135 ppt. Above the 4.0 ppt legal limit in at least one sample. Compliance is judged on a running annual average, not one sample.
  • PFHxS (above the health goal) was found in 80 of 121 samples, highest 80 ppt. Above the 10 ppt legal limit in at least one sample. Compliance is judged on a running annual average, not one sample.
  • PFOA (above the health goal) was found in nine of 121 samples, highest 18.3 ppt. Above the 4.0 ppt legal limit in at least one sample. Compliance is judged on a running annual average, not one sample.
  • Lead (above the health goal) In the latest period, 9 in 10 homes sampled were at or below 1.7 ppb, below the 15 ppb action level. The action level drops to 10 ppb on Nov. 1, 2027. EPA’s health goal for lead is zero.

No health-based violations on file since 2016.

What handles it

What was found

Highlighted: above the health goal, or EPA’s health benchmark where there is no goal. Circled: above the legal limit in at least one sample, or the action level. Every scale puts that line at its middle.

PFAS and lithium: EPA UCMR 5, samples taken from Sept. 4, 2023 to Dec. 18, 2025. Each blue tick on a scale is one sample where it was found.

Lead and copper: EPA SDWIS monitoring periods ending 2022. The pointer marks the latest period; each blue tick is an earlier one.

NSF’s PFAS claims are tested to below 20 ppt. EPA’s limit is 4.0 ppt, and EPA says no certification yet shows a filter reaching its levels.

Copper (above the health goal)

Comes from pipes, often your own

170 (above the action level)ppm

90th percentile, 2020 to 2022

In the latest period, 9 in 10 homes sampled were at or below 170 ppm, above the 1.3 ppm action level.

What handles it

PFOS (above the health goal)

Comes from the source

135 (above the legal limit in at least one sample)ppt

Highest of 121 samples; found in 37

Above the 4.0 ppt legal limit in at least one sample. Compliance is judged on a running annual average, not one sample.

What handles it

PFHxS (above the health goal)

Comes from the source

80 (above the legal limit in at least one sample)ppt

Highest of 121 samples; found in 80

Above the 10 ppt legal limit in at least one sample. Compliance is judged on a running annual average, not one sample.

What handles it

PFOA (above the health goal)

Comes from the source

18.3 (above the legal limit in at least one sample)ppt

Highest of 121 samples; found in nine

Above the 4.0 ppt legal limit in at least one sample. Compliance is judged on a running annual average, not one sample.

What handles it

Lead (above the health goal)

Comes from pipes, often your own

1.7ppb

90th percentile, 2023 to 2025

In the latest period, 9 in 10 homes sampled were at or below 1.7 ppb, below the 15 ppb action level. The action level drops to 10 ppb on Nov. 1, 2027. EPA’s health goal for lead is zero.

What handles it

PFBS

Comes from the source

34.9ppt

Highest of 121 samples; found in 43

Below EPA’s hazard index benchmark of 2,000 ppt. PFBS has no legal limit or health goal of its own.

What handles it

Also found, with no federal limit

EPA measured these PFAS to learn how often they occur. None has a legal limit or a health goal yet.

CompoundHighest sampleFound inCertification claim
6:2 FTS148 ppt5 of 121None covers it
PFPeA47.5 ppt66 of 121None covers it
PFHxA37.1 ppt56 of 121None covers it
PFHpA18.5 ppt22 of 121NSF/ANSI 53: Total PFAS Reduction
PFBA18.1 ppt8 of 121None covers it
PFPeS9.9 ppt4 of 121None covers it
8:2 FTS7.5 ppt1 of 121None covers it

Tested and not found

Below EPA’s minimum reporting level in every sample taken from Sept. 4, 2023 to Dec. 18, 2025. Not found means not measured above that level, which is not the same as zero.

All 19 compounds tested and not found
  • 11Cl-PF3OUdS
  • 4:2 FTS
  • 9Cl-PF3ONS
  • ADONA
  • HFPO-DA (GenX)
  • Lithium
  • NEtFOSAA
  • NFDHA
  • NMeFOSAA
  • PFDA
  • PFDoA
  • PFEESA
  • PFHpS
  • PFMBA
  • PFMPA
  • PFNA
  • PFTA
  • PFTrDA
  • PFUnA

Violations since 2016

No health-based violations on file with EPA since 2016.

What handles it

A certification covers specific claims, not a whole standard. Look for these claims on the certifier’s listing, not the box. Wording varies a little: NSF writes “Lead Reduction,” WQA just “Lead.”

  • NSF/ANSI 53

    Claims: Copper Reduction, PFOS Reduction, Total PFAS Reduction, PFOA Reduction, Lead Reduction

    Other certifiers’ wording: Perfluorooctane Sulfonate (PFOS); Perfluorohexane Sulfonic Acid (PFHxS); Perfluorooctanoic Acid (PFOA)

    For: Copper, PFOS, PFHxS, PFOA, Lead

  • NSF/ANSI 58

    Claims: Copper Reduction, Perfluorooctane Sulfonate (PFOS), Perfluorooctanoic Acid (PFOA), Lead Reduction

    For: Copper, PFOS, PFOA, Lead

At the tap, or for the whole house?

Lead and copper usually come from pipes and fixtures inside or near your home. A whole-house system sits where water enters, so it cannot catch what your own plumbing adds after it. For those, the filter that counts is the one at the tap. How whole-house systems compare.

Compare five-year costs

Filters with those claims on a certifier’s listing

TapBuff earns a commission if you buy through some links on this page. It does not change which standard or filter we name. As an Amazon Associate, TapBuff earns from qualifying purchases. How TapBuff makes money

What this report cannot tell you

  • Levels of everything else. Federal bulk data carries results for PFAS, lithium, lead and copper, and violations for the rest. Nitrate, arsenic, disinfection byproducts and other levels are in Gwa Northern Water System’s own annual report, which it must send you every year.
  • Your own plumbing. Lead results are the 90th percentile across homes the utility samples. Your home’s service line, solder and fixtures decide yours. A certified lab test is the only way to know.
  • Anything after the latest data. SDWIS data is from 2026 Q2; UCMR 5 samples are from Sept. 4, 2023 to Dec. 18, 2025.

Other Guam utilities

All Guam utilities

Sources

What to do next

  • Read up on the 5 marked results

    What each one does to health, where it comes from, and the certification claim that addresses it.

    Start with Copper

  • Get the utility’s own report

    Gwa Northern Water System must send you a water quality report every year. It lists nitrate, arsenic and byproduct levels this page cannot.

    How to read it

  • Test your own tap for lead

    Your service line, solder and fixtures decide the lead at your faucet, not the utility’s average.

    Lead in your water: what to do

  • Compare certified filters

    What the filters certified for these results cost over five years, cartridges included.

    Compare five-year costs