Honolulu’s drinking water comes from Honolulu Board of Water Supply (Windward-Pearl Harbor) (EPA system HI0000331), which pumps groundwater from wells and treats it before distribution for about 631,389 people. EPA’s records associate 11 sizeable community systems with Honolulu; Honolulu Board of Water Supply (Windward-Pearl Harbor) is the main one, and it is the system this page examines in depth. This page translates that system’s official EPA record — lead and copper results, violation history, and what the data does and does not say — into plain English.
This page is built entirely from the U.S. EPA’s Safe Drinking Water Information System (SDWIS), the same records state regulators use. We did not test Honolulu’s water, and system-level data describes the utility’s water as a whole — not what comes out of one specific home’s tap. Where the record is silent, we say so rather than guess.
Key takeaways
- Honolulu Board of Water Supply (Windward-Pearl Harbor) supplies Honolulu (Groundwater); it serves about 631,389 people across its service area.
- In the most recent sampling reported to the EPA, Honolulu Board of Water Supply (Windward-Pearl Harbor)’s 90th-percentile lead result was not detected — reported as 0 ppb against an EPA action level of 15 ppb.
- No health-based violations in the last 10 years of EPA records for Honolulu Board of Water Supply (Windward-Pearl Harbor).
- EPA does not track hardness. If you’re shopping for a softener, test first and size from a real grains-per-gallon number.
The water system serving Honolulu
Honolulu Board of Water Supply (Windward-Pearl Harbor) is the community water system the EPA associates with Honolulu, Hawaii. It reports a population served of about 631,389.
| System | EPA ID | People served | Source water | Role |
|---|---|---|---|---|
| Honolulu Board of Water Supply (Windward-Pearl Harbor) | HI0000331 | 631,389 | Groundwater | Main system |
| Waipahu-Ewa-Waianae | HI0000335 | 217,479 | Groundwater | Also serves the area |
| Mililani | HI0000367 | 50,573 | Groundwater | Also serves the area |
| Wahiawa | HI0000333 | 23,348 | Groundwater | Also serves the area |
| Waipio Heights | HI0000334 | 11,516 | Groundwater | Also serves the area |
| Waialua-Haleiwa | HI0000332 | 9,996 | Groundwater | Also serves the area |
EPA’s records associate 9 further systems with the Honolulu area beyond the ones above — neighbourhood districts, subdivisions and mobile-home parks among them. If your water bill names a different system, that name — not the city name — is the record to check.
Not sure which system serves your address? Run your ZIP code through our What’s In My Water? lookup — it resolves the systems EPA lists for your ZIP and shows the same records in full.
Lead and copper
Lead: in the most recent sampling reported to the EPA, Honolulu Board of Water Supply (Windward-Pearl Harbor)’s 90th-percentile lead result was not detected — reported as 0 ppb against an EPA action level of 15 ppb.
Read those numbers carefully: a 90th percentile is a system-wide statistic from a sample of homes, not a test of your tap. Lead in drinking water comes mostly from a home’s own plumbing — service lines, solder and fixtures — so two houses on the same street can test very differently. Homes built before 1986 carry the highest risk, whatever the system average says.
Violation history — the last 10 years
EPA records show no health-based violations for Honolulu Board of Water Supply (Windward-Pearl Harbor) in the last 10 years. Health-based violations are the serious kind: a contaminant over its legal limit, a skipped treatment step, or a disinfectant level above its maximum.
The recent paperwork record is clean too: no monitoring or reporting items in the last 5 years.
What this means for your home
System data sets the background; your home’s plumbing writes the foreground. In practice:
- Lead is a plumbing question, not a system alarm, here. The system’s own result is low, so the remaining risk sits in your home’s pipes and fixtures. A filter certified to NSF/ANSI 53 for lead is cheap insurance for older homes; our water filter guides explain the certifications without the marketing.
- Hardness is not in this record — by design. The EPA doesn’t track it, so nobody can honestly tell you your grains-per-gallon from this page. Scale on fixtures and shower doors is a hint, not a measurement. Test (strips are a start; a lab test is better — see how to test your water at home), then size any softener with our softener sizing calculator and the softener hub.
- On a private well instead of city water? None of this system’s record applies to your tap — start with our well water hub for the test-first approach.
Water quality in nearby cities
New York, NY · Los Angeles, CA · Houston, TX
This guide is one of our per-city water reports — see the full list on the Water Quality hub, alongside our contaminant explainers and testing guides.
Frequently asked questions
Is Honolulu water safe to drink?
On the evidence in its EPA record, yes: Honolulu Board of Water Supply (Windward-Pearl Harbor) has no health-based violations in the last 10 years, and its most recent 90th-percentile lead result was not detected, against an action level of 15 ppb. Health-based violations are the serious category — the contamination and treatment failures — so a clean 10-year record is the strongest signal the federal data offers. Two honest limits: EPA data describes the system as a whole, not your tap, and lead in particular usually comes from a home’s own plumbing — a certified home test is the only way to know your exact water.
Where does Honolulu get its drinking water?
Honolulu Board of Water Supply (Windward-Pearl Harbor) is the community water system the EPA associates with Honolulu. It pumps groundwater from wells and treats it before distribution and serves about 631,389 people across its service area (EPA system ID HI0000331). 10 other sizeable systems also report serving parts of Honolulu — they are listed in the table above.
What is the lead level in Honolulu’s water?
In the most recent sampling reported to the EPA, Honolulu Board of Water Supply (Windward-Pearl Harbor)’s 90th-percentile lead result was not detected (0 ppb), against an action level of 15 ppb. That is a system statistic from sampled homes, not a test of your tap — older home plumbing can still add lead on the last few metres, which is why a home test beats any average if your house predates 1986.
Has Honolulu’s water system had violations?
No health-based violations appear for Honolulu Board of Water Supply (Windward-Pearl Harbor) in the last 10 years of EPA records. Its recent monitoring and reporting record is clean as well.
Do I need a water filter in Honolulu?
Nothing in Honolulu Board of Water Supply (Windward-Pearl Harbor)’s EPA record points to a problem you must filter for. Most households here who filter do it for taste (a simple carbon filter) or for lead insurance in older plumbing (NSF/ANSI 53). If you shop, match the certification to the job — and measure hardness before considering a softener.
Source: U.S. EPA SDWIS via Envirofacts, retrieved November 11, 2026. System-level data describes the utility’s water, not any individual tap. If your water bill names a different system, that system’s record is the one that applies to you.