Mililani
EPA ID: HI0000367 · 50,573 people served · 1 ZIP code
ZipCheckup's reading of EPA SDWIS for Mililani (HI0000367): no EPA violations recorded in the last five years. In every reporting cycle over the past five years, Mililani has come through without a single EPA violation - a consistent performance across the full service population of approximately 50,573 residents that reflects both well-maintained infrastructure and reliable operational oversight.
Data: EPA SDWIS
Service Area Map
Coverage area for Mililani Source: EPA SDWIS service area boundaries.
Service area boundary - Grade A
Service Area Demographics
The Mililani serves a community with a median household income of $125,822 and an estimated 54,608 residents across its service area. 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 pumped from underground aquifers. 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
Estimated Remediation Costs
Average estimated costs across ZIP codes served by this system
Based on national averages for common remediation projects. Actual costs vary by property. Only issues flagged by EPA, FEMA, or state data for each ZIP code are included.
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 |
|---|---|---|
| 0 mg/L | No | N/A |
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
Dominant radon zone for ZIP codes served by this system: Zone 3 (Low Risk)
Need help with your water quality?
Typical cost: Water test: typically $20–$50 (DIY kit) · Professional inspection: $150–$400
Find the Right Water FilterFree tip: Let cold water run for 2 minutes before drinking — this helps flush lead from your pipes.
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 the full compliance record 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: Tested Clean
This water system was tested under the federal EPA Unregulated Contaminant Monitoring Rule (UCMR5). No PFAS compounds were detected.
Current MCL reflects the lowest state-enforceable limit (NYS 10 ppt for PFOA/PFOS, effective August 2020). The federal final MCL of 4 ppt for PFOA/PFOS (EPA April 2024 rule) is not enforceable until April 2029. Detections above 4 ppt but below 10 ppt are below current MCL but above the future federal limit.
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/}
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