Mililani, HI Water Safety: 73/100 (2026)
1 ZIP code · 3 water systems · Updated 2026-06-04
Tap water in Mililani, HI scores well — low violation counts, above-average safety grade.
How Mililani Compares
Data: EPA SDWIS Last verified: 2026-06-04
Key Facts for Mililani Residents
- Homes built before 1986: 51% — older plumbing may contain lead solder.
- Estimated remediation: $1,200 per household.
- CDC health risk index: 10.63.
Mililani's Water Providers
In Mililani, HI, residential water supply is distributed across multiple utilities rather than concentrated in one. The 3 leading providers out of 3 tracked systems each control their own infrastructure, file separate EPA compliance reports, and set independent rate schedules.
Overview
We track water quality and home safety data for 1 ZIP code in Mililani, Hawaii, covering 3 community water systems serving approximately 54,608 people.
No EPA violations recorded across any ZIP codes in Mililani — an excellent indicator of water quality.
Home Safety Score
Average Home Safety Score for Mililani: B (73/100)
The score combines three factors:
| Factor | What It Measures |
|---|---|
| Water Quality | EPA violations and compliance history |
| Lead Levels | 90th percentile lead concentration vs EPA action level |
| Radon Risk | EPA radon zone classification |
Water Sources
Mililani water systems draw from: Groundwater.
Lead & Copper
- Lead data: not yet available for Mililani
- 0 ZIP codes exceed the EPA lead action level
Radon Risk
Dominant radon zone: Zone 3 (Low Risk)
Areas with No Violations
| ZIP Code | Safety Score | System | Population |
|---|---|---|---|
| 96789 | B | Mililani | 50,573 |
All ZIP Codes in Mililani
- 96789 [B]
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Lead/copper: EPA Lead and Copper Rule sampling data
- Radon: EPA Map of Radon Zones
Updated daily.
Mililani Community Health Snapshot
Source: CDC PLACES (County-level estimates). Water contamination can correlate with respiratory and chronic health conditions.
Compared to National Average
Vertical line = national average. ■ Above national · ■ Below national
Mililani Infrastructure Age
With 51% of homes built before 1986, lead solder in plumbing is a potential concern. The EPA banned lead solder in 1986, but many older homes retain original plumbing.
Source: U.S. Census Bureau American Community Survey (ACS).
Housing Age Profile
Reading the housing age data for Mililani — median build year 1984 — the overriding implication is that the plumbing materials inside a typical home here reflect pre-1986 construction standards. In practical terms, that means lead-soldered copper joints are common across much of the housing stock. Where those materials are present, water can leach lead as it moves through joints — a pathway that corrosion control treatment under federal rules is designed to reduce, though it cannot eliminate lead risk where the plumbing materials themselves contain lead.
Over half of homes in Mililani were built before 1986, when lead solder was banned. Older plumbing may leach lead into drinking water, especially with corrosive water chemistry.
Source: U.S. Census Bureau ACS B25034.
How Remediation Costs Compare in Mililani
Low proportionality — that's the Mililani picture when remediation costs are placed against typical home equity.
Remediation costs in Mililani are relatively low compared to home values. The $800–$1,800 estimated range is a small fraction of median property value. Home values are 20% above the Hawaii average.
Mililani: Lead Risk & Vulnerable Populations
Why children are most at risk: The CDC states there is no safe level of lead exposure for children. Children under 6 absorb lead more readily than adults, and even low levels can cause developmental delays, learning difficulties, and behavioral problems.
Pulling a tap sample fills the gap that utility data cannot close, particularly here where 51% of housing dates from the pre-rule era and citywide monitoring sits at or above the regulatory mark in Mililani.
Sources: EPA Lead and Copper Rule, U.S. Census Bureau ACS, CDC childhood lead poisoning prevention guidelines.
Mililani: Flood History & Water Damage Risk
FEMA data shows 100% of Mililani's ZIP codes mapped into designated flood zones, paired with an NFIP record of 6 claims. That footprint places local flood exposure in the range where it warrants attention without rising to high-severity planning territory.
Mililani has a moderate flood history with 6 FEMA claims averaging $18,017 per payout. 100% of ZIP codes fall within FEMA flood zones. Flood events can contaminate drinking water and overwhelm treatment systems.
How flooding affects water quality: Flood events can introduce sewage, agricultural runoff, and industrial chemicals into water supplies. Even after floodwaters recede, contamination can persist in wells and aging infrastructure. Flood damage can add significantly to the estimated <strong>$1,200</strong> remediation cost per household.
Residents in flood-prone areas should consider flood insurance even outside FEMA zones — over 25% of flood claims come from low-to-moderate risk areas. After any flood event, test your water before drinking.
Source: FEMA National Flood Insurance Program (NFIP) claims data, FEMA flood zone designations.
Deep Dive Reports
Detailed analysis for Mililani, HI