King County Water District #20
EPA ID: WA5338950 · 48,469 people served · 6 ZIP codes
ZipCheckup's reading of EPA records for King County Water District #20 (WA5338950): no drinking-water violations recorded since 2021. Zero violations are listed in EPA monitoring data for King County Water District #20; a count of records like this is not a water-quality test for the 48,469 residents it serves.
Data: EPA SDWIS
Service Area Map
Coverage area for King County Water District #20 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 King County Water District #20 have a median household income of $99,633 and about 148,715 residents live in those ZIP codes (Census; not the number of people this system supplies). Approximately 69% of housing stock was built before 1986, which increases the likelihood of lead service lines and older plumbing.
🌊 Where Does Your Water Come From?
King County Water District #20'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.
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
King County Water District #20 (EPA ID: WA5338950) is a community water system in Washington that serves approximately 48,469 people from surface water sources.
This system provides water to 6 ZIP codes across 1 community.
ZIP-Area Home Safety Context: A (100/100)
This is the average Home Safety Score for 1 of 6 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
No reported lead measurement appears for this PWSID in the accepted LCR snapshot. Absence of a reported measurement is not a measured zero.
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
6 of 6 ZIP records with known zones are 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 WA or modeled from parcel and building-footprint data.
Data Sources
This report uses public data from the EPA Safe Drinking Water Information System (SDWIS). View available EPA compliance records for King County Water District #20 (WA5338950) on EPA.gov.
Frequently Asked Questions
Is King County Water District #20 water safe to drink?
The accepted 2026Q2 ECHO snapshot contains zero violation records for King County Water District #20 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 King County Water District #20 serve?
King County Water District #20 serves approximately 48,469 people across 6 ZIP codes in Washington.
Where does King County Water District #20 get its water?
The primary water source is surface water.
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.). King County Water District #20, WA: Serves 48K People. https://zipcheckup.com/water-system/wa5338950/
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