City of Mercer Island
EPA ID: WA5353640 · 30,689 people served · 1 ZIP code
Water monitoring history at City of Mercer Island shows a clean slate — EPA tracking over the past five years turned up no violations, and 30,689 residents continue to receive fully compliant service.
Data: EPA SDWIS Last verified: 2026-04-02
Service Area Map
Coverage area for City of Mercer Island Source: EPA SDWIS service area boundaries.
Service area boundary — Grade A
Service Area Demographics
The City of Mercer Island serves a community with a median household income of $202,359 and an estimated 25,282 residents across its service area. Approximately 67% of housing stock was built before 1986, which increases the likelihood of lead service lines and older plumbing.
🌊 Where Does Your Water Come From?
City of Mercer Island's water is drawn from rivers, lakes, or reservoirs. Surface water sources are more exposed to agricultural runoff, stormwater, and upstream discharges, but they typically receive more intensive treatment before reaching your tap.
About 2% of homes in King County, Washington rely on private wells rather than public water systems. Private well owners are responsible for their own water testing and treatment.
Superfund Proximity Note: This service area ranks in the 70th percentile nationally for proximity to Superfund (NPL) sites.
Infrastructure Risk
Comparable Water Systems
Similar-sized systems in Washington
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
City of Mercer Island (EPA ID: WA5353640) is a community water system in Washington that serves approximately 30,689 people from surface water sources.
This system serves ZIP code 98040 in Mercer Island.
Average Home Safety Score: A (87/100)
Based on water quality violations, lead levels, and radon risk across all ZIP codes served by this system.
Violation History
Lead & Copper
EPA Lead and Copper Rule sampling data for ZIP codes served by this system:
| ZIP Code | Lead Level | Exceeds Limit | Sample Date |
|---|---|---|---|
| 98040 | 0.0063 mg/L | No | N/A |
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 WA or modeled from parcel and building-footprint data.
- 98040 — Mercer Island
Data Sources
This report uses public data from the EPA Safe Drinking Water Information System (SDWIS). View the full compliance record for City of Mercer Island (WA5353640) on EPA.gov.
Frequently Asked Questions
Is City of Mercer Island water safe to drink?
Based on EPA records, City of Mercer Island has no recorded violations in the past 5 years — a positive indicator of water quality management.
How many people does City of Mercer Island serve?
City of Mercer Island serves approximately 30,689 people across 1 ZIP code in Washington.
Where does City of Mercer Island get its water?
The primary water source is surface water.
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 →
Lead Service Line Inventory
Service line breakdown reported under the federal Lead and Copper Rule Improvements (LCRI) inventory requirement:
This system reports zero confirmed lead service lines in its inventory. Unknown-material counts may still warrant verification.
Federal LCRI rule (effective October 2024) requires every public water system to inventory its service lines and complete lead-line replacement within 10 years.
Source: EPA SDWIS Federal Service Line Inventory (Phase 2) · Submitted 2026
ZipCheckup is not affiliated with the utility or state agency. Inventory figures render verbatim from the public LCRI submission cited above; ZipCheckup does not perform inspections or replacements.