Mililani
EPA ID: HI0000367 · 50,573 people served · 1 ZIP code
ZipCheckup's reading of EPA records for Mililani (HI0000367): no drinking-water violations recorded since 2021. Mililani's compliance file in EPA SDWIS lists no violations, whether health-based or monitoring and reporting, for a utility that supplies water to approximately 50,573 residents.
Data: EPA SDWIS
Service Area Map
Coverage area for Mililani Source: EPA SDWIS service area boundaries.
Service area boundary - average Home Safety grade of mapped ZIPs: A
Demographics of ZIP Codes Served
The ZIP codes associated with Mililani have a median household income of $125,822 and about 54,608 residents live in those ZIP codes (Census; not the number of people this system supplies). Approximately 51% of housing stock was built before 1986, which increases the likelihood of lead service lines and older plumbing.
💧 Where Does Your Water Come From?
Mililani's water is classified in EPA records as a groundwater source. Groundwater is naturally filtered through rock and soil, but it can be vulnerable to PFAS contamination, nitrates from agriculture, and industrial chemicals that seep into the water table.
Superfund Proximity Note: This service area ranks in the 60th percentile nationally for proximity to Superfund (NPL) sites. Groundwater sources near contaminated sites may face elevated risk from industrial chemicals.
Infrastructure Risk
Comparable Water Systems
Similar-sized systems in Hawaii
System Overview
Mililani (EPA ID: HI0000367) is a community water system in Hawaii that serves approximately 50,573 people from groundwater sources.
This system serves ZIP code 96789 in Mililani.
ZIP-Area Home Safety Context: A (100/100)
This is the average Home Safety Score for 1 of 1 service-area ZIP codes with all required score domains observed. It is not a grade for the water utility.
Model 4.0.0 uses SDWIS identity plus accepted ECHO SDWA lifecycle-based water compliance, the UCMR 5 PFAS MCL screen, EPA radon zone, and annual EPA AirData AQI across three equally weighted domains. Missing required evidence suppresses the score.
Violation History
Lead & Copper
EPA Lead and Copper Rule evidence attributed directly to this water system:
| Lead Level | Exceeds Action Level | Sample Date |
|---|---|---|
| Below the reporting limit | No | 2018-12-31 |
No copper action-level exceedance record appears for this PWSID in the accepted LCR snapshot. This does not establish a clean copper measurement.
Radon Risk in Service Area
1 of 1 ZIP records with known zones is in EPA Radon Zone 3.
The EPA recommends testing all homes regardless of radon zone. County radon zones cannot replace an in-home radon test.
ZIP Codes Served
Coverage: Service area ZIP codes sourced from EPA Community Water System Service Area Boundaries v3 (March 2026 release). These ZIPs reflect the actual deployment footprint recorded by HI or modeled from parcel and building-footprint data.
- 96789 - Mililani
Data Sources
This report uses public data from the EPA Safe Drinking Water Information System (SDWIS). View available EPA compliance records for Mililani (HI0000367) on EPA.gov.
Frequently Asked Questions
Is Mililani water safe to drink?
The accepted 2026Q2 ECHO snapshot contains zero violation records for Mililani in the inclusive 2021-2026 record-year window. This is a compliance-record finding, not a guarantee about water at a specific tap.
How many people does Mililani serve?
Mililani serves approximately 50,573 people across 1 ZIP code in Hawaii.
Where does Mililani get its water?
The primary water source is groundwater.
Federal UCMR5 PFAS Monitoring: No PFAS Reported Above Reporting Levels
This water system was tested under the federal EPA Unregulated Contaminant Monitoring Rule (UCMR5). No PFAS compounds were reported above UCMR5 minimum reporting levels.
EPA's April 2024 PFAS rule sets MCLs of 4 ppt for PFOA and PFOS and 10 ppt for PFHxS, PFNA and HFPO-DA (GenX); water systems must comply from 2029. Other PFAS compounds have no individual federal MCL. A state standard is shown only where this system's state has its own enforceable PFAS limit. Detection results are EPA UCMR5 samples, not a measurement at your tap.
Source: U.S. EPA UCMR5 (Unregulated Contaminant Monitoring Rule, 5th cycle) — per-system federal sampling, 2023–2025. EPA UCMR5 monitoring program →
How Water Systems Appear in Rankings
Water systems are evaluated by violation history, contaminant detections, and service population. Larger systems with more service connections appear in more rankings.
Frequently Asked Questions
How to cite this page
ZipCheckup. (n.d.). Mililani, HI: Serves 51K People. https://zipcheckup.com/water-system/hi0000367/
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author = {{ZipCheckup}},
title = {{Mililani, HI: Serves 51K People}},
year = {n.d.},
url = {https://zipcheckup.com/water-system/hi0000367/}
}