Mercer Island, WA Water Safety: 87/100 (2026)
1 ZIP code · 2 water systems · Updated 2026-06-04
Throughout Mercer Island and across its water systems, EPA compliance data for WA shows above-average performance — violations are minimal, none of the tracked systems have recorded repeated MCL exceedances in recent cycles, and the safety picture has held steady across multiple reporting periods.
How Mercer Island Compares
Data: EPA SDWIS Last verified: 2026-06-04
Key Facts for Mercer Island Residents
- Average lead level: 0.0063 mg/L.
- Homes built before 1986: 67% — older plumbing may contain lead solder.
- Estimated remediation: $1,200 per household.
- CDC health risk index: 8.82.
Mercer Island's Water Providers
2 independent water providers serve Mercer Island, WA — 2 systems appear in federal records.
Overview
We track water quality and home safety data for 1 ZIP code in Mercer Island, Washington, covering 2 community water systems serving approximately 25,282 people.
No EPA violations recorded across any ZIP codes in Mercer Island — an excellent indicator of water quality.
Home Safety Score
Average Home Safety Score for Mercer Island: A (87/100)
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
Mercer Island water systems draw from: Groundwater, Surface water.
Lead & Copper
- Average lead level (90th percentile): 0.0063 mg/L (EPA action level: 0.015 mg/L)
- 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 |
|---|---|---|---|
| 98040 | A | City of Mercer Island | 30,689 |
All ZIP Codes in Mercer Island
- 98040 [A]
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.
Mercer Island 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
Mercer Island Infrastructure Age
With 67% 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
Lead solder was standard in copper plumbing until federally banned in 1986; lead pipes were common in service lines pre-1970. Mercer Island's median build year of 1976 reflects a housing stock where these older materials are a pervasive feature — not a rare legacy — of the residential plumbing landscape.
Over half of homes in Mercer Island 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 Mercer Island
Given current Mercer Island valuations, the remediation-to-property-value ratio is low — most homeowners are looking at a proportionally modest share that fits within routine financial planning.
Remediation costs in Mercer Island are relatively low compared to home values. The $800–$1,800 estimated range is a small fraction of median property value. Home values are 303% above the Washington average.
Mercer Island: 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.
Older stock in Mercer Island represents 67% of the inventory, and citywide monitoring runs at or above the federal action level — making an in-home read a standard household-level step.
Sources: EPA Lead and Copper Rule, U.S. Census Bureau ACS, CDC childhood lead poisoning prevention guidelines.
Mercer Island: Flood History & Water Damage Risk
Flood risk in Mercer Island occupies the middle ground: 13 NFIP claims and 100% of local ZIP codes within FEMA flood zones. At that level, the risk pathways connecting flooding to water quality — treatment system stress, well infiltration, distribution backflow — become relevant considerations during significant flood events, even if day-to-day water quality is unaffected by flood history.
Mercer Island has a moderate flood history with 13 FEMA claims averaging $10,462 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 Mercer Island, WA