Washington Water Quality Deep Dive - 4,465 Systems Analyzed

Executive Summary

Washington's state laboratory corpus covers 4,465 public water systems and contains 34,741 laboratory records, including 7,747 quantified measurements. Separately, 422 ZIP codes have a direct EPA water-system mapping in this analysis. Of the laboratory records, 7,338 have an applicable limit or action level for comparison. The corpus identifies 93 quantified threshold exceedances and 70 separately reported action-level exceedance records. Censored, non-detect and unknown records are not counted as measured zero, and no overall rate is reported across incompatible record types.

The state's primary water quality challenges center on PFAS from military installations and agricultural nitrate in the Yakima Valley. Geographic risk patterns across Washington reflect PFAS contamination from military installations including McChord-Lewis and Fairchild AFB, nitrate from Yakima Valley agriculture, naturally occurring arsenic in some volcanic geology areas, and lead in Seattle's older housing.

This report is not a summary - it is a ground-level examination of what the data actually shows. Every number comes from EPA SDWIS enforcement records, state laboratory testing programs, Consumer Confidence Reports filed by utilities, FEMA flood insurance claims, and Census Bureau housing stock data. Where the data tells a clear story, we state it plainly. Where it is ambiguous or incomplete, we note that too.

Contaminant Analysis

State laboratory testing and EPA monitoring data reveal the scope of contamination across Washington's water supply. The following analysis covers both regulated contaminants with federal MCLs and state-specific standards - Washington set state action levels for PFAS before EPA established MCLs; DOH has been proactive on PFAS monitoring and has conducted comprehensive statewide testing.

Top Contaminants by Applicable Threshold Exceedance Rate

How to read the copper row. EPA's federal reporting schema defines the CU90 code as a Copper Action Level Exceedance: the record exists only where a system's 90th-percentile copper result was at or above the 1.3 mg/L action level. Every copper record in this dataset is therefore an exceedance, which is why no rate is shown - there is no denominator of clean copper results to compute one from. For the same reason, a system with no copper record has not been shown to be clean: non-exceedance copper results are optional to report for systems serving 3,300 people or fewer. We do not publish a copper level because the same schema transmits no verified unit of measure for this code.

Copper appears here differently from every other contaminant in the table. EPA's federal database records a copper 90th-percentile result under the CU90 code specifically when it exceeds the 1.3 mg/L action level, so Washington's 70 copper records across 32 systems are 70 action-level exceedances, not a sample of routine copper testing. Copper leaches from the same plumbing that leaches lead - household pipes, solder and fixtures - and the corrosion control that keeps one in check is what keeps the other in check. Read the count, not a rate: there is no reported population of clean copper results to divide by, and a system missing from this line has not been shown to be clean, only to have reported nothing.

PFAS ("Forever Chemicals") in Washington

PFAS monitoring in Washington covers 13,188 laboratory records across multiple PFAS compounds. This corpus contains quantified PFAS measurements, but those records do not carry an applicable threshold for comparison. Their threshold-exceedance status therefore cannot be determined from this dataset.

For detailed PFAS data by ZIP code, see the PFAS in Washington report.

State vs. Federal Standards

Washington set state action levels for PFAS before EPA established MCLs; DOH has been proactive on PFAS monitoring and has conducted comprehensive statewide testing.

This regulatory landscape creates a two-tier compliance reality. A water system in Washington may appear "in compliance" on federal reports while actually exceeding stricter state limits. For residents reading their annual Consumer Confidence Report, this distinction matters enormously - the report may reference federal standards while the state is enforcing tighter ones.

The gap between state and federal standards also affects how threshold exceedances are counted. Our dataset captures both tiers. Lead and copper use action-level terminology; other rows identify a federal MCL or state standard where available. "Applicable threshold" is not a claim that every threshold is an MCL.

Worst Water Systems by Violations

The following systems had the highest number of applicable-limit or action-level exceedance records in our dataset. A critical caveat: exceedance count alone does not mean a system is currently unsafe. Many exceedances are resolved through treatment adjustments, blending, or switching water sources. However, repeated patterns across multiple contaminants or years can indicate systemic issues that warrant closer review.

FOUR SEASONS PARK leads with 4 exceedances in our dataset. HAYNES ACRES DIVISION 1 follows with 4 exceedances.

If you receive water from any of these systems, we recommend checking your specific ZIP code report for the most current violation status and filtration recommendations. Exceedance data tells you what has happened - your ZIP report tells you what to do about it.

Of Washington's 4,465 monitored systems, the 10 systems with the most records account for 28 of the state's 163 applicable-threshold or action-level exceedance records. This is a historical corpus concentration, not a current safety ranking.

Enforcement & Compliance

EPA and state enforcement records can show how documented violations move through warnings, compliance schedules, formal orders, and court actions. ZIPs without a canonically matched enforcement record are excluded rather than counted as clean.

Among enforcement actions in the covered records, 4% are formal and 96% are informal. This describes corpus coverage, not statewide enforcement intensity.

The covered records report 73 unresolved violations. ZIPs without a complete direct-match enforcement record are not included. PFAS contamination near military bases drove some of the earliest state-level PFAS action; Yakima Valley nitrate contamination has prompted major agricultural best-practice initiatives.

Areas with Most Health Violations

Geographic Risk Patterns

Water quality risk in Washington is not evenly distributed. PFAS contamination from military installations including McChord-Lewis and Fairchild AFB, nitrate from Yakima Valley agriculture, naturally occurring arsenic in some volcanic geology areas, and lead in Seattle's older housing create distinct regional patterns that are visible in the data.

Understanding where water quality problems concentrate is as important as understanding what contaminants are present. A statewide average conceals enormous ZIP-to-ZIP variation - two communities 20 miles apart may have completely different risk profiles based on their water source, treatment infrastructure, and local geology.

Data Anomalies & Notable Findings

Our automated anomaly detection system flagged 8+ patterns worth investigation in Washington:

High-severity findings:

• ZIP 98448 (severity 8/10): PFAS cluster: 3 adjacent ZIPs near Tacoma, WA all exceed limits - View full report
• ZIP 98660 (severity 8/10): PFAS cluster: 5 adjacent ZIPs near Vancouver, WA all exceed limits - View full report
• ZIP 98668 (severity 8/10): PFAS cluster: 3 adjacent ZIPs near Vancouver, WA all exceed limits - View full report

Lead Exposure & Infrastructure Age

Lead contamination in drinking water is almost never caused by the water source itself - it leaches from lead service lines, lead solder in copper pipes, and brass fixtures as water sits in contact with these materials. This means lead risk is fundamentally an infrastructure problem, and infrastructure age is the single strongest predictor.

In Washington, Puget Sound metro growth straining water systems while eastern Washington agricultural communities face nitrate treatment challenges; many small systems serve growing suburban areas. The federal Lead and Copper Rule (LCR) requires utilities to test a sample of high-risk homes and report the 90th percentile lead level - meaning 90% of samples must be below the 15 ppb action level. But this sampling methodology has long been criticized: utilities often avoid the worst homes, and the action level itself is not a health-based standard (the EPA has stated there is no safe level of lead exposure).

Across Washington, 371 ZIP codes have elevated or high lead pipe risk based on housing age, and 132 have elevated electrical system risk. These infrastructure age indicators are derived from Census Bureau American Community Survey data on housing stock vintage.

The connection between housing age and water contamination risk is well-documented: homes built before 1986 (when the federal ban on lead solder took effect) are significantly more likely to have lead in their plumbing. Homes built before 1950 face even higher risk, as lead service lines were standard construction practice in many parts of the country during that era.

Highest Lead Exposure Risk ZIP Codes

Flood Risk & Water Infrastructure

Flooding directly threatens water quality through multiple mechanisms: overwhelmed treatment plants release partially treated water, floodwaters can infiltrate well heads and contaminate groundwater sources, damaged distribution lines create entry points for bacteria and sediment, and power outages disable treatment systems entirely. In the aftermath of major flood events, boil-water advisories become common - but many residents in affected areas may not receive timely notification.

• 452 ZIP codes in Washington have FEMA flood insurance claims on record
• 15,837 total flood insurance claims filed historically
• $364.5 million sum of reported building, contents, and ICC payment components
• 12,872 claims with payment data; 2,965 claims without reported payment fields

The average reported payment-component sum among claims with payment data in Washington is $28,320. Missing payment fields are not treated as zero. While flood damage is typically associated with structural property damage, the water quality implications are often overlooked. Communities with repeated flooding face compounding infrastructure degradation - each event weakens pipes, treatment facilities, and distribution systems that may not be fully restored before the next event.

Consumer Confidence Reports (CCRs)

Water utilities are required to publish annual Consumer Confidence Reports. We have parsed CCR data for 220 ZIP codes in Washington. The legacy violation fields do not have source-bound evidence, so we do not publish a violation count from them. Violation status remains unknown for 67 water systems. Legacy lead values are also withheld until their measurement evidence is accepted.

CCR data is self-reported by utilities and may undercount actual contamination events. Cross-referencing CCR data with EPA SDWIS violation records provides a more complete picture - which is exactly what ZipCheckup reports do for every ZIP code.

Trend Analysis & Regulatory Outlook

PFAS contamination near military bases drove some of the earliest state-level PFAS action; Yakima Valley nitrate contamination has prompted major agricultural best-practice initiatives.

Three major regulatory forces are reshaping water quality across Washington and the country:

Lead and Copper Rule Improvements (LCRI): The 2024 LCRI represents the most significant update to lead regulation since the original 1991 rule. It requires all water systems to complete a lead service line inventory, lower the action level trigger from 15 ppb to 10 ppb, and replace all lead service lines within 10 years. For Washington's 4,465 systems, this means billions in infrastructure investment - and a fundamental reshaping of the lead risk landscape we document above.

PFAS National Primary Drinking Water Regulation (2024): For the first time, EPA set enforceable MCLs for six PFAS compounds - PFOA and PFOS at 4 ppt, and four others at various levels. Systems nationwide are still in the initial monitoring phase, which is why our PFAS data captures detections that may not yet have triggered formal violations. Treatment to remove PFAS (primarily granular activated carbon or reverse osmosis) is expensive, and many small systems will struggle to comply within the 3–5 year implementation timeline.

State-level action: Washington set state action levels for PFAS before EPA established MCLs; DOH has been proactive on PFAS monitoring and has conducted comprehensive statewide testing. As federal regulation catches up to state standards in some areas, the patchwork of requirements creates an uneven compliance landscape that makes cross-state comparisons complex but ZIP-level analysis essential.

What Washington Residents Should Do

Based on our analysis of 34,741 laboratory records and 726 ZIP codes, here are specific actions for Washington residents:

1. Check your ZIP code report - enter your ZIP at ZipCheckup.com to see contaminant data, violation history, and risk scores specific to your address
2. Request your utility's CCR - if your ZIP is not in our CCR database, request the latest Consumer Confidence Report directly from your water utility
3. Test your water independently - home water testing kits ($30–$150) can detect lead, bacteria, and common contaminants. Lab testing ($100–$400) provides more comprehensive results
4. Consider filtration - for the contaminants most prevalent in Washington (PFAS, Lead, Nitrate), reverse osmosis or NSF-certified carbon filters provide the most effective protection
5. Check for lead service lines - if your home was built before 1986, contact your utility to determine if you have a lead service line. Many utilities now offer free inspections
6. Prepare for flood events - if you're in a flood-prone area, keep bottled water reserves and know how to shut off your water main. After any flood, do not use tap water until your utility confirms safety

Methodology & Data Sources

This analysis combines multiple data sources:

• EPA SDWIS - Safe Drinking Water Information System violation and enforcement records
• State laboratory data - WA — Lead & Copper 90th Percentile (EPA ECHO LCR); WA — PFAS Monitoring (UCMR5 National Dataset); WA — SDWIS Health-Based Violations (EPA Envirofacts); WA — Community Water Systems (EPA SDWIS) (34,741 records)
• EPA ECHO - Enforcement and Compliance History Online, including PFAS detections and enforcement actions
• Consumer Confidence Reports - parsed and cross-referenced with EPA data for 220 ZIP codes
• FEMA NFIP - National Flood Insurance Program claims data
• Census ACS - Housing age and demographic data for infrastructure risk modeling
• Lead exposure modeling - ZipCheckup's proprietary lead risk score combining housing age, water test results, and service line data

All data is updated regularly. This report reflects data available as of 2026-08-31.

Related Reports

• Washington State Overview - ZIP rankings, county breakdown, and safety scores
• PFAS in Washington - detailed contaminant breakdown
• Lead in Washington - detailed contaminant breakdown
• Nitrate in Washington - detailed contaminant breakdown
• Arsenic in Washington - detailed contaminant breakdown
• Home Safety Score Rankings by State - compare Washington to other states

Highest-Risk ZIP Codes in Washington

• 98586 South Bend Water Report - Lead: 23 ppb
• 98941 Roslyn Water Report - Lead: 13 ppb
• 99030 Rockford Water Report - Lead: 20.8 ppb
• 98577 Raymond Water Report - Lead: 23 ppb
• 98537 Cosmopolis Water Report - Lead: 23 ppb

@misc{zipcheckup-states-washington-deep-dive,
  author = {{ZipCheckup}},
  title  = {{Washington Water Quality Deep Dive - 4,465 Systems Analyzed}},
  year   = {2026},
  url    = {https://zipcheckup.com/states/washington/deep-dive/}
}