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Community Water System · PWS GU0000006

Gwa Northern Water System

Mangilao, Guam 96913 - drinking water served from groundwater sources to 139,207 people, tracked in EPA SDWIS and UCMR5.

139,207
People served
30
EPA violations
6
Health-based
11 PFAS
UCMR5 result

The verdict

EPA records 30 drinking-water violations at Gwa Northern Water System, 20% of them health-based - above the Guam per-system average, and UCMR5 testing detected 11 PFAS compounds.

30
Total EPA violations on record
20%
Health-based (MCL / treatment failure)
139,207
People served by this system
11
PFAS compounds detected (UCMR5)

Water Quality Snapshot: Gwa Northern Water System

Gwa Northern Water System is a state-owned community water system that delivers drinking water to 139,207 residents in Mangilao, Guam (Guam County) through 39,541 service connections. Its water is drawn from groundwater sources. EPA's Safe Drinking Water Information System records 30 total violations for this system , of which 6 (20%) are health-based, meaning a contaminant exceeded an EPA Maximum Contaminant Level or a required treatment technique failed. The most recent violation on record dates to 1985.

The most frequently cited contaminant at this system is Mercury, recorded in 6 violations (MCL, health-based). Under EPA's UCMR5 PFAS monitoring program, 11 PFAS compounds were detected in samples collected from this system, with a maximum reported concentration of 148.2 ppt (parts per trillion). PFAS are persistent synthetic chemicals linked to health effects at very low exposure levels.

Across Guam, EPA tracks 8 public water systems serving 327,417 people, with 203 cumulative violations and 94 health-based violations on record. About 100% of systems in the state carry at least one violation, and state-wide the average per system is 25.4 violations. Statewide, 3 of 5 UCMR5-tested systems have reported PFAS detections (60%).

Gwa Northern Water System's 30 violations sit above the Guam average.

All figures above are sourced directly from EPA SDWIS and UCMR5 public data releases and are updated as EPA publishes new reporting cycles.

PFAS Detected

11 PFAS "forever chemicals" detected in testing under EPA's UCMR5 monitoring program.

Population Served
139,207
Total Violations
30
Health-Based Violations
6
Water Source
Groundwater

System Details

System Type
Community
Owner Type
State
Connections
39,541
County
Guam
School/Daycare
No
MCL Violations
6
Monitoring Violations
0
Treatment Tech Violations
0

Violation History

Contaminant violations recorded by EPA.

Contaminant Category Count Latest
Mercury MCL 6 1985

PFAS Testing Results (UCMR5)

Results from EPA's Fifth Unregulated Contaminant Monitoring Rule. 323 of 3335 samples detected PFAS.

Contaminant Date Result MRL Status
PFBA 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
NMeFOSAA 9/7/2023 <6.00 ppt 6.00 ppt Not Detected
PFMBA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
PFEESA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
NFDHA 9/7/2023 <20.00 ppt 20.00 ppt Not Detected
PFPeS 9/7/2023 <4.00 ppt 4.00 ppt Not Detected
NEtFOSAA 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
PFTA 9/7/2023 <8.00 ppt 8.00 ppt Not Detected
HFPO-DA 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
6:2 FTS 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
PFDoA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
PFTrDA 9/7/2023 <7.00 ppt 7.00 ppt Not Detected
PFHpS 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
PFMPA 9/7/2023 <4.00 ppt 4.00 ppt Not Detected
4:2 FTS 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
ADONA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
9Cl-PF3ONS 9/7/2023 <2.00 ppt 2.00 ppt Not Detected
11Cl-PF3OUdS 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
PFHxA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
PFDA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
PFOA 9/7/2023 <4.00 ppt 4.00 ppt Not Detected
PFOS 9/7/2023 <4.00 ppt 4.00 ppt Not Detected
PFNA 9/7/2023 <4.00 ppt 4.00 ppt Not Detected
PFPeA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
PFHpA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
PFHxS 9/7/2023 3.60 ppt 3.00 ppt Detected
PFUnA 9/7/2023 <2.00 ppt 2.00 ppt Not Detected
8:2 FTS 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
PFBS 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
NMeFOSAA 9/7/2023 <6.00 ppt 6.00 ppt Not Detected
PFTrDA 9/7/2023 <7.00 ppt 7.00 ppt Not Detected
NEtFOSAA 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
PFTA 9/7/2023 <8.00 ppt 8.00 ppt Not Detected
NMeFOSAA 9/7/2023 <6.00 ppt 6.00 ppt Not Detected
PFTrDA 9/7/2023 <7.00 ppt 7.00 ppt Not Detected
NEtFOSAA 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
PFTA 9/7/2023 <8.00 ppt 8.00 ppt Not Detected
PFMBA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
HFPO-DA 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
PFBA 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
6:2 FTS 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
4:2 FTS 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
8:2 FTS 9/7/2023 <5.00 ppt 5.00 ppt Not Detected
ADONA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
PFPeA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
PFUnA 9/7/2023 <2.00 ppt 2.00 ppt Not Detected
PFEESA 9/7/2023 <3.00 ppt 3.00 ppt Not Detected
NFDHA 9/7/2023 <20.00 ppt 20.00 ppt Not Detected
PFPeS 9/7/2023 <4.00 ppt 4.00 ppt Not Detected
PFHpS 9/7/2023 <3.00 ppt 3.00 ppt Not Detected

Verify This Water System

The figures above are aggregated from EPA's public databases. To verify the underlying records, or to file a complaint, request a Consumer Confidence Report, or check current monitoring status, go directly to the federal and state regulators that enforce the Safe Drinking Water Act for Gwa Northern Water System.

Federal Source of Truth

EPA SDWIS, Federal Reports

EPA's Safe Drinking Water Information System (SDWIS) holds the federal compliance record for every regulated public water system. Open the system-level report by PWS ID:

View PWS ID GU0000006 on SDWIS

Source: EPA SDWIS Federal Reports Search

State Regulator

Guam Drinking Water Authority

Guam's primacy agency administers the Safe Drinking Water Act locally. Search EPA SDWIS for the current state contact, or use the state's public health or environment department portal.

Find GU regulator via EPA SDWIS

Violation Timeline

Each row links to the EPA SDWIS public record for verification. Cross-reference the contaminant code on EPA's federal report to see violation dates, return-to-compliance status, and enforcement actions.

Year (latest) Contaminant Category Count EPA Record
1985 Mercury MCL 6 SDWIS / GU0000006 / 1035

How Gwa Northern Water System Compares

Cross-reference this system's record against state averages and the federal MCL framework for context.

Metric Gwa Northern Water System Guam avg Federal benchmark
Total violations 30 25.4 SDWA compliance, any non-zero count is a recorded breach
Health-based violations 6 11.8 Indicates a contaminant exceeded a federal MCL
PFAS detection 11 compounds 60% EPA final rule (2024): PFOA/PFOS MCL = 4.0 ppt
Population served 139,207 40,927 Sizing context for compliance burden

Sources: EPA SDWIS and EPA National Primary Drinking Water Regulations (40 CFR Part 141). State averages computed across 8 regulated public water systems in Guam.

Federal MCL reference, Safe Drinking Water Act thresholds ▼
Contaminant Federal MCL / Action Level Note
Lead 0 mg/L (Action Level: 0.015 mg/L) Lead and Copper Rule treatment technique
Arsenic 0.010 mg/L (10 ppb) Health-based MCL since 2006
Total Coliform Treatment technique (RTCR) Indicator organism, monitoring trigger
PFOA / PFOS (PFAS) 4.0 ppt each (final 2024 rule) Compliance deadline 2029 (EPA proposed extending to 2031, not yet final as of May 2026)
Nitrate (as N) 10 mg/L Acute health risk for infants

Frequently Asked Questions

Is Gwa Northern Water System water safe to drink? ▼
Gwa Northern Water System (PWS ID: GU0000006) has 30 recorded violations in the EPA SDWIS database. PFAS contamination has been detected in UCMR5 testing, with 11 PFAS compounds found. This system serves 139,207 people using Groundwater sources.
How many people does Gwa Northern Water System serve? ▼
Gwa Northern Water System serves 139,207 people in Mangilao, Guam. It is a State-owned system using Groundwater water sources with 39,541 service connections.
What type of violations does Gwa Northern Water System have? ▼
Gwa Northern Water System has 30 total violations: 6 health-based violations (MCL exceedances or treatment failures), 0 monitoring/reporting violations, and 0 treatment technique violations. Health-based violations indicate contaminant levels exceeded EPA safe limits.
Has PFAS been detected in Gwa Northern Water System water? ▼
Yes. UCMR5 testing detected 11 PFAS compounds in Gwa Northern Water System's water supply: PFHxS, PFPeA, PFHxA, PFBS, PFHpA, and others. PFAS are persistent "forever chemicals" that do not break down in the environment.
What water source does Gwa Northern Water System use? ▼
Gwa Northern Water System uses Groundwater as its primary water source. It is classified as a Community Water System (CWS), serving residential populations year-round.
Where does this data come from? ▼
All data comes from the EPA Safe Drinking Water Information System (SDWIS) and the UCMR5 PFAS monitoring program. SDWIS tracks compliance for all public water systems regulated under the Safe Drinking Water Act.
Data Sources: EPA Safe Drinking Water Information System (SDWIS), Q4 2025. PFAS data from EPA UCMR5 monitoring program (2023-2025). This data is provided for informational purposes only.

Read our methodology - how this data is sourced, computed, and verified.

Data sourced from EPA SDWIS and UCMR5 PFAS monitoring data. See our methodology for details. Retrieved and formatted by PlainWater Editorial

Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This system's figures are rendered directly from EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.