Guam Waterworks Authority – Northern Water System water quality
Mangilao, GU · serves 139,207 people (39,541 connections) · Groundwater · State · EPA ID GU0000006
Data: U.S. EPA · How we read the data · How we check it
Summary
PFAS above the 2024 federal limits. Systems have until 2029 to meet the PFAS limits.
Is it an emergency? No: PFAS limits are about years of exposure, not a glass of water, and nothing in EPA's data calls for you to stop drinking the water today. If your utility ever issues a boil-water or do-not-drink notice, follow it.
- PFAS
- Above limitPFOA, PFOS, PFHxS, the PFAS Hazard Index above the federal limit in EPA's 2023–2025 testing (PFOA 13.4 ppt vs a limit of 4 ppt, PFOS 67.5 ppt vs a limit of 4 ppt, PFHxS 40 ppt vs a limit of 10 ppt, where ppt = parts per trillion).
- Lead
- Below action level1.7 ppb (parts per billion) at the 90th percentile: 9 in 10 homes sampled were at or below it. Action level 15 ppb, falling to 10 ppb in Nov 2027. Monitoring period ending Dec 2025. Your home's pipes can make yours higher.
- Violations
- None health-basedNo health-based violations since 2016.
- Pregnant, or mixing baby formula with tap water? Babies drink more water for their size, so PFAS exposure matters more for them. Consider bottled water or a filter certified for PFAS for formula, and ask your doctor. Health effects.
- To lower your PFAS exposure now, a home filter certified for PFAS reduction works (reverse osmosis, or activated carbon certified to NSF/ANSI 53 or 58). Filters for these results.
- Built before 1986, or not sure what your service line is made of? Check your service line and test your tap. Utility data can't show your pipes.
- Tested your own tap? Compare your result with these numbers. Moving? Compare this system with another.
- Read Guam Waterworks Authority – Northern Water System's annual water quality report (Consumer Confidence Report). It lists every regulated contaminant tested and is usually on the utility's website or mailed with your bill, and you can also request it at (671) 300-6845. EPA: how to find it.
PFAS (“forever chemicals”)
EPA UCMR 5: 61 entry points tested Sep 2023 to Dec 2025. "Average" is the highest entry-point average (non-detects counted as zero), the way EPA compares UCMR 5 results to the limits. ppt = parts per trillion. These results do not determine compliance.
| Contaminant | Highest average |
|---|---|
| PFOA Above limit Limit 4 ppt | 13.4 ppt 3.35× the limit |
| PFOS Above limit Limit 4 ppt | 67.5 ppt 16.9× the limit |
| PFHxS Above limit Limit 10 ppt | 40 ppt 4× the limit |
| PFNA Not detected Limit 10 ppt | – |
| HFPO-DA (GenX) Not detected Limit 10 ppt | – |
| Hazard Index (a combined score for PFHxS, PFNA, GenX and PFBS, where above 1 is over the limit) Above limit Limit 1 | 4 |
| PFBS Detected, below limit Guideline 2,000 ppt | 32.3 ppt |
| PFBA Detected, below limit Guideline 6,000 ppt | 15.1 ppt |
| PFHxA Detected, below limit Guideline 3,000 ppt | 30.8 ppt |
| PFPeA Detected, no limit | 40.6 ppt |
| PFHpA Detected, no limit | 15.7 ppt |
| PFPeS Detected, no limit | 4.95 ppt |
| 6:2 FTS Detected, no limit | 108 ppt |
| 8:2 FTS Detected, no limit | 3.75 ppt |
29 PFAS tested, 11 detected at least once. "Not detected" means below EPA's reporting limit (about 2 to 20 ppt depending on the chemical), not proven zero. PFAS not listed were not detected. The limits for PFHxS, PFNA, GenX and the Hazard Index were proposed for rescission in May 2026. That proposal is not final. Systems have until 2029 to meet the limits.
Lithium
Not detected in 121 samples (reporting limit 9 ppb). About lithium.
Lead and copper
Latest 90th percentile: 1.7 ppb lead (Jan 2023 – Dec 2025). Below action level
Highest since 2016: 2.5 ppb (Dec 2022).
| Monitoring period | Lead (90th pct.) |
|---|---|
| Jan 2023 – Dec 2025 | 1.7 ppb |
| Jan 2020 – Dec 2022 | 2.5 ppb |
| Jan 2017 – Dec 2019 | 1.9 ppb |
Earlier results (5)
| Jan 2003 – Dec 2003 | 6 ppb |
| Jul 2002 – Dec 2002 | 5.7 ppb |
| Jan 2002 – Jun 2002 | 6.4 ppb |
| Jul 1992 – Dec 1992 | 11 ppb |
| Jan 1992 – Jun 1992 | 24.6 ppb |
Lead comes from pipes and fixtures, not the source water, so it varies home to home. The 90th percentile means 9 in 10 sampled homes were at or below it. More on lead.
Violations
Health-based violations mean a contaminant exceeded a limit or a required treatment step was missed. Monitoring and reporting violations mean required tests or reports were late or missing, so the water's quality during that time is unknown. The total includes every violation in EPA's records, most of them paperwork.
Earlier EPA testing (2013–2020)
| Contaminant | Highest | Guideline |
|---|---|---|
| Manganese | 9.5 ppb | 300 ppb |
| Chlorate | 28 ppb | 210 ppb |
| Chromium-6 | 26 ppb | – |
| Vanadium | 3 ppb | 21 ppb |
| Strontium | 0.96 ppm | 1.5 ppm |
| 1,4-Dioxane | 0.71 ppb | 0.35 ppb |
Where it serves
ZIP codes the system reported serving: 96910, 96913, 96915, 96929, 96932
Questions
Is Guam Waterworks Authority – Northern Water System water safe to drink?
Guam Waterworks Authority – Northern Water System has no health-based violations since 2016. EPA testing found PFAS above the 2024 federal limits, which systems must meet by 2029. Federal data can't tell you about your own pipes: lead comes from service lines and plumbing, so test your tap if your home was built before 1986. For the official word, read the utility's annual Consumer Confidence Report.
Does Guam Waterworks Authority – Northern Water System water have PFAS?
Yes. EPA's 2023–2025 testing of Guam Waterworks Authority – Northern Water System found 11 PFAS at least once. The highest entry-point averages were above the federal limit for PFOA and PFOS and PFHxS: PFOA 13.4 ppt, PFOS 67.5 ppt, PFHxS 40 ppt (limit 4 ppt for PFOA and PFOS, 10 ppt for the others).
What is the lead level in Guam Waterworks Authority – Northern Water System water?
The most recent 90th-percentile lead result for Guam Waterworks Authority – Northern Water System is 1.7 ppb, for the period ending Dec 2025. The federal action level is 15 ppb, falling to 10 ppb in November 2027. The 90th percentile means 9 in 10 homes sampled were at or below this number. Individual homes can be higher.
Check these numbers yourself
Every figure on this page comes from public EPA records. You don't have to take our word for it:
- EPA's own report for GU0000006: violations, enforcement and inspections, straight from EPA.
- EPA UCMR 5 data: the PFAS and lithium results (search the file for PWSID GU0000006).
- EPA SDWIS download: the lead results, population and violation records we use.
- The utility's annual water quality report (Consumer Confidence Report): ask Guam Waterworks Authority – Northern Water System at (671) 300-6845, or see EPA's guide to finding it.
Found something that doesn't match? Tell us and we'll check it against EPA's records. How we check our data.
Source: U.S. EPA drinking water records and PFAS testing (UCMR 5). How we read the data.