Public water system · HI0000367
ActiveMililani
At a glance
Mililani (PWSID HI0000367) is an active community water system in Honolulu County, Hawaii. It reports serving 50,573 people through 11,915 service connections. Its primary water source is groundwater, and EPA lists it as owned by a local government. Of the 12 most recent violations in EPA's records, none is health-based, and the most recent began in April 2000.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
50,573
Service connections
11,915
Primary source
GW
Groundwater
System type
CWS
Community water system
System record
How does Mililani compare with other water systems in Honolulu County?
By EPA's size categories, Mililani is a large system (10,001 to 100,000 people). Honolulu County has 38 active public water systems, and Mililani is the 4th-largest of them by population served. Its population served is about 70% above the county average of 29,687 people per system, and accounts for 4.5% of the 1,128,119 people reported by systems filed under the county. Across Hawaii, the 136 active systems average 11,181 people each. Nationally, the average active community water system reports serving 6,703 people, so Mililani is about 7.5 times that figure.
What does “community water system” mean?
A community water system serves at least 15 connections used by year-round residents, or regularly serves at least 25 year-round residents. Homes, apartments and mobile-home parks are served by these. Hawaii has 119 active community water systems, 88% of the state's 136 active systems. Groundwater means the system draws its water from wells or springs fed by underground aquifers. 112 Hawaii systems (82%) list groundwater as their primary source.
Who owns and regulates Mililani?
EPA lists Mililani as owned by a local government. The HI state drinking water program is its primacy agency, the regulator with primary enforcement responsibility for the system under the Safe Drinking Water Act. 8 of the 38 active systems in Honolulu County (21%) are also owned by a local government.
Does Mililani have drinking water violations?
Of the 12 most recent violations in EPA's records, none is health-based, and the most recent began in April 2000. The violations listed here began between July 1997 and April 2000. By type: 12 monitoring and reporting. The contaminant or rule involved most often is Total coliform bacteria (TCR) (12 of them). EPA lists 12 as archived. Archived means the violation was not marked resolved but is more than five years past the end of the noncompliance period, so it no longer counts toward current compliance status.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2000-04-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 2000-01-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1999-10-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1999-07-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1999-04-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1999-01-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1998-10-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1998-07-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1998-04-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1998-01-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1997-10-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
| 1997-07-01 | Monitoring and reportingMonitoring, Routine Minor (TCR) · code 24 | Total coliform bacteria (TCR)code 3100 | No | Archived |
The 12 most recent violations in EPA's records, newest first.Labels and codes come from EPA's SDWIS reference tables. A monitoring or reporting violation means a required test or report was missed or late; it does not by itself mean a contaminant was found. "Health-based" marks violations of a legal limit or required treatment.
Mililani: frequently asked questions
Who runs Mililani?
Mililani (PWSID HI0000367) is a community water system owned by a local government. It is regulated by the HI state drinking water program.
How many people does Mililani serve?
Mililani reports serving 50,573 people through 11,915 service connections in Honolulu County, Hawaii.
Where does Mililani get its water?
EPA SDWIS lists this system's primary water source as groundwater. Groundwater means the system draws its water from wells or springs fed by underground aquifers.
Does Mililani have any drinking water violations?
Of the 12 most recent violations in EPA's records, none is health-based, and the most recent began in April 2000. A monitoring or reporting violation means a required test or report was missed or late; it does not by itself mean a contaminant was found.
Is Mililani's water safe to drink?
AquaCensus shows EPA compliance records, not current water test results, so it cannot say whether the water is safe at a given moment. Of the 12 most recent violations in EPA's records, none is health-based, and the most recent began in April 2000. For current results, consult the system's annual water quality report, EPA ECHO, or the HI state drinking water program.
Where can I find Mililani's water quality report?
As a community water system, Mililani must deliver an annual water quality report, called a Consumer Confidence Report, to its customers by July 1 each year, covering the previous calendar year. The system can provide a copy on request.
Other water systems in Honolulu County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Hnl-Windward-Pearl Harbor | Honolulu | 631,389 | Community | Groundwater |
| Waipahu-Ewa-Waianae | Honolulu | 217,479 | Community | Groundwater |
| Joint Base Pearl Harbor-Hickam | Honolulu | 65,230 | Community | Groundwater |
| Schofield Barracks | Honolulu | 37,920 | Community | Groundwater |
| Wahiawa | Honolulu | 23,348 | Community | Groundwater |
| Marine Corps Base Hawaii | Honolulu | 16,300 | Community | Purchased groundwater |
Related pages
Working with water-system records? Pro adds alerts, change history and CSV export ($49/mo); Enterprise adds full national files, the API and an MCP server for AI tools.
About this data
Source: U.S. EPA Safe Drinking Water Information System (SDWIS) and SDWA violation records, via EPA ECHO, as published October 1, 2026 — AquaCensus refreshes it quarterly. See the methodology for how records are matched, cleaned and scored.
Cite as: AquaCensus, “Mililani, PWSID HI0000367, Hawaii”, https://aquacensus.com/water-systems/hawaii/mililani-hi0000367 (data as of October 1, 2026).