waterbycounty
Compiled federal source snapshot

Washington Water Quality

Drinking water data for all 38 counties.

Avg SDWIS Compliance Index

58.6

Most Common Five-Year SDWIS Compliance Band

C

Counties with Data

38

of 38 total

County water atlas

Washington water signals by county

A state-level 2.5D view across drinking-water compliance, watershed impairment, monitoring density, and streamflow snapshot context. Pin any county, switch layers, then use the lens controls to compare index ranges, recorded violation rates, or impaired watersheds without leaving the page.

Counties

38

Avg SDWIS index

58.6

Watersheds

0

ATTAINS counties

Monitoring

38

26 fresh USGS snapshots

State atlas layers combine EPA SDWIS health-based violations, EPA ATTAINS 303(d) impairment assessments, EPA Water Quality Portal monitoring sites, and representative USGS NWIS streamflow gauges. Streamflow values appear only for fresh pipeline snapshots, not as a continuously updated stream. County pages include the observation time and year.

Prepared by ByCounty Editorial TeamPublished by WaterByCounty

Multi-source coverage in Washington

Beyond Drinking Water

EPA SDWIS

38/ 38

counties with drinking-water compliance data

476 health violations statewide (5yr)

EPA ATTAINS

—

No §303(d) assessments yet for Washington

EPA WQP

4,450

monitoring sites across 38 counties

1,465,168 total readings (5yr window)

USGS NWIS

26

counties with a fresh pipeline snapshot

1 above25 below

State atlas notes

What stands out in Washington

County water quality is not one number. The strongest read comes from comparing drinking-water compliance against watershed impairment, monitoring density, and streamflow context. Use these signals as a starting point, then open any county profile for source-level detail.

Compliance spread

Asotin County has the highest value in the published state SDWIS Compliance Index table at 86.2/100, while Ferry County has the lowest at 1.1/100. That is a 85.1 point gap inside one state.

Zero health violations

7

3+ health violations

20

Monitoring hubs

Thurston County813 sitesSkagit County668 sitesKitsap County635 sites

Lowest flow reads

Walla Walla County3%Lincoln County4%Whitman County4%

Highest fresh streamflow pipeline snapshots: Kittitas County (150%, observation 2026), Stevens County (80%, observation 2026), Clark County (77%, observation 2026). These are source-data observations, not household tap-water conclusions.

All Washington Counties

CountySDWIS Compliance Index
Asotin County86.2
Columbia County86.2
Cowlitz County86.2
Douglas County86.2
Lincoln County86.2
Pend Oreille County86.2
Whitman County86.2
Snohomish County72.3
King County71.7
Clark County70.7
Kitsap County70.7
Spokane County67.4
Chelan County66.3
Mason County66.3
Skagit County65.9
Yakima County65.9
Pierce County65.1
Clallam County64.5
Jefferson County64.5
Kittitas County63.6
Franklin County58.6
Grays Harbor County55.9
Klickitat County55.9
Benton County55.4
Adams County55.2
Pacific County55.2
Thurston County55.2
Lewis County50.5
Skamania County50.5
Okanogan County49.9
Whatcom County48.4
Walla Walla County48.3
Grant County46.4
Stevens County41.2
Garfield County7.5
Island County6.9
San Juan County5.1
Ferry County1.1

Frequently Asked Questions

Which Washington county has the highest SDWIS Compliance Index?
Asotin County has the highest SDWIS Compliance Index in the published Washington cohort at 86.2/100. This WaterByCounty relative comparison is not an EPA score and does not establish current conditions for a utility or address.
What does the Five-Year SDWIS Compliance Band mean?
The band is derived only from each county aggregation's recorded health-violation rate per 100,000 people served for the stated five-year source window. It is separate from the relative SDWIS Compliance Index and is not a current determination for a specific utility or address.
Which USGS streamflow records are shown across Washington?
WaterByCounty has 26 fresh USGS pipeline snapshots in the published Washington cohort. Each county page shows its observation timestamp and year. A pipeline snapshot is not a continuously updated reading or a tap-water safety measure.
Where can Washington residents find current official information?
Review the applicable utility's Consumer Confidence Report, active notices, and the state drinking-water agency. WaterByCounty's county-level historical aggregations do not establish the current status of a specific utility, address, private well, or household plumbing system.
What does Water Quality Portal monitoring volume show in Washington?
The published county records contain 1,465,168 results from 4,450 monitoring locations in the site's five-year aggregation. Monitoring volume does not by itself indicate better or worse water quality.

Data Sources

Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. The WaterByCounty SDWIS Compliance Index reflects the recorded rate and is not an EPA score.

Disclaimer: This data is informational only. It is not health, legal, or professional advice. For concerns about your specific water supply, contact your local water utility.

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