waterbycounty
Federal water data

County water report

King County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for King County, Washington.

Water grade

A

Water score

71.1

State rank

#11

of 39

Health violations

16

EPA SDWIS, 5-year lookback

Watershed impaired

Not reported

EPA ATTAINS coverage varies by state

Monitoring sites

253

39,669 recent measurements

Live streamflow

104%

SNOQUALMIE RIVER NEAR CARNATION, WA

Water at a glance

Key Water Indicators for King County

EPA SDWIS

Safety Grade

A

Score: 71.1 / 100

EPA SDWIS

Active Violations

16

5-year health-based lookback

EPA ATTAINS

Watershed Health

Not reported

Coverage varies by state

USGS NWIS

Streamflow Snapshot

104% of mean

SNOQUALMIE RIVER NEAR CARNATION, WA

EPA WQP

Monitoring Sites

253

39,669 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

A

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

71.1/100

Health violations

16

Health-based violations

Violations per 100K served

0.5

Population-normalized SDWIS rate

Data center water stress

King County has 15 facilities in the DCWSI dataset.

ByCounty's DCWSI ranks this county #36 nationally by combining its water score with mapped data center density.

DCWSIThe Data Center Water Stress Index: 60% the county's water-system stress plus 40% how concentrated data centers already are, scored 0-100. Higher means data-center density and water pressure overlap more here.

78.8

0-100 index

Facility count

15

90.3 density percentile

Discharge estimate

Not reported

EPA CWA fields where available

Water vs median

+21.1

Compared with US county median

Named operators

EquinixSabeyDigital RealtyComcastH5 Data Centers

Mapped facilities

  • CTI Biopharma

    Seattle

    OSM

  • Equinix SE3 Data Center

    Seattle · Equinix

    OSM

  • Intergate Seattle East Building 1

    Sabey

    OSM

  • Intergate Seattle East Building 2

    Tukwila

    OSM

  • Intergate Seattle East Building 3

    Tukwila · Sabey

    OSM

  • Intergate Seattle East Building 4

    Tukwila · Digital Realty

    OSM

9 more mapped facilities included in the county score.

See the King County data-center reportReview methodology

Data Center Water Budget Calculator

Estimate daily water use for a hypothetical facility in King County.

1 MW1,000 MW
40%100%
799K gallons/dayModerate Impact

Your facility would use 12.7% of this county's industrial water baseline — manageable but worth monitoring against drought trends.

12.7% of county industrial baseline5.48 Mgal/day remaining headroom

Based on USGS 2020 water-use data and EPA-standard cooling intensity constants. Not a substitute for site-specific water rights analysis.

Editorial analysis

Understanding King County’s Water

Drinking Water Quality Overview

EPA SDWIS

King County earns an A grade for drinking water quality, scoring 71.1 out of 100. Over the past five years, EPA SDWIS records 16 health-based violations — a pattern that public water utilities are required to disclose and correct.

River & Streamflow Status

USGS NWIS

USGS NWIS gauge data (as of 2026-05-14T11:15:00.000-07:00) puts SNOQUALMIE RIVER at 3.9k cfs — near its historical average at 104% of mean flow. Streamflow is a leading indicator of drought stress, sediment load, and dilution capacity: low flows concentrate pollutants and warm water temperatures, stressing aquatic life and, in surface-water-dependent systems, the source water quality for treatment plants.

Monitoring Network

EPA WQP

EPA's Water Quality Portal (WQP) aggregates monitoring data from federal, state, and tribal agencies. King County has extensive coverage with 253 active monitoring sites with 39,669 recent measurements on record. Predominant monitoring categories include physical and organics, pesticide. More monitoring sites generally indicate greater scientific attention to local water conditions — and provide the baseline data that regulators use to set future impairment listings.

Editorial advisory

What the data suggests for King County

Water Verdict

King County, Washington receives a good water quality assessment with a grade of A and a score of 71.1 out of 100. While the water supply is generally safe, occasional monitoring gaps or minor contaminant detections may occur. The county's primary USGS gauge drains roughly 603 square miles of upstream watershed, giving local source waters a regional footprint. At the most recent USGS reading, local streamflow was tracking near its historical mean (103.6%).

Violation Context

EPA SDWIS records for King County, Washington show 16 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 0.5 violations per 100,000 people served, this rate is relatively low compared to many U.S. counties. This compliance record sits alongside an unusually deep monitoring archive: 39,669 water-quality results have been logged across the county in the EPA Water Quality Portal over the past five years.

Consumer Guidance

Tap water compliance data for King County shows a A grade. King County's drinking-water compliance score is 71.1 out of 100. Reviewing your utility's most recent Consumer Confidence Report provides the most accurate picture of detected contaminants and treatment status. An NSF-certified water filter can add an extra layer of safety for any household concerns. A pipeline streamflow snapshot from the SNOQUALMIE RIVER gauge is also available on this page.

Regional Context

King County has better water quality than the average county in Washington. Its water score is 11.8 points higher than the state average, indicating stronger water system performance relative to neighboring counties.

Advisory text summarizes county-level public records and is not a replacement for your utility's current Consumer Confidence Report or direct local notices.

Contaminants & Resources

Key issues flagged in King County's water environment

Official EPA Resources for King County

EPA How's My Waterway

Interactive watershed health data for King County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for King County

Consumer Confidence Reports (WA)

Annual water quality reports from utilities in Washington

Past 5 years

Water Quality Monitoring

Monitoring Sites

253

Active in the past 5 years

Measurements Recorded

40K

39,669 total readings

Most Measured

  • Physical
  • Organics, Pesticide
  • Not Assigned

Categories measured most frequently

Data from the EPA Water Quality Portal (WQP), aggregating monitoring records from federal, state, and tribal sources. Each measurement represents a single sample analyzed for a specific characteristic (e.g., E. coli, pH, dissolved oxygen, nitrogen).

Live USGS Streamgage

River & Stream Conditions

Current Discharge

3,860cfs

May 14, 6:15 PM UTC

vs Long-Term Average

104%

Near typical

Primary Streamgage

SNOQUALMIE RIVER NEAR CARNATION, WA

USGS site
12149000
Drainage area
603 sq mi
Long-term mean
3,724 cfs

One representative streamgage (the one with the largest drainage area in the county). Many counties have multiple gauges; this view summarizes the primary one. The long-term mean is the full-record annual average; the percent-of-typical value compares the latest reading against that average.

Free tool

Estimate Your Water Costs

Water Cost Estimate

3

3 people  ·  ~225 gal/day

Annual Total

$558

Monthly

$47

Water Bill

$558/yr

Filter Cost

$0/yr

Safety Grade for King County:C — Moderate

Some violations or watershed impairment detected.

Estimates use the national average residential water rate ($0.0068/gal, EPA/AWWA 2023) and EPA WaterSense per-person consumption baseline (75 gal/person/day). Actual bills vary by utility, usage tier, and local infrastructure fees. For informational purposes only.

Try the full calculator →

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Frequently Asked Questions

What is the water quality in King County, Washington?
King County, Washington has a drinking-water quality grade of A with a score of 71.1/100, based on EPA SDWIS compliance data. The county has 16 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and streamflow snapshots are reported separately on this page.
Are there any water violations in King County?
King County has 16 health-based drinking water violations recorded by the EPA over the past 5 years. Health-based violations indicate instances where contaminant levels exceeded EPA Maximum Contaminant Levels (MCLs). Violations may have been resolved — check with your local water utility for current status.
How much water-quality monitoring happens in King County?
EPA's Water Quality Portal records 39,669 measurements from 253 monitoring sites in King County over the past five years. The most frequently measured characteristic groups are Physical, Organics, Pesticide, Not Assigned. Each measurement is a single sample analyzed for one characteristic (E. coli, pH, dissolved oxygen, etc.). High monitoring density means more scientific evidence behind any reported signal — it does not by itself indicate water quality.
What's happening with rivers in King County right now?
King County's primary USGS streamgage on the SNOQUALMIE RIVER has a pipeline snapshot of 3,860 cubic feet per second — 104% of the long-term mean of 3,724.48 cfs. Flow is within typical range for this gauge. For the latest gauge feed, visit waterdata.usgs.gov.
How does King County water compare to the Washington average?
King County's SDWIS water quality score of 71.1/100 is higher than the Washington state average of 59.3. The average water quality grade across Washington is D, based on data from 39 counties with available SDWIS data.
Is tap water safe to drink in King County?
Based on EPA SDWIS data, King County has a water quality grade of A (71.1/100). This indicates good to excellent water quality with strong SDWIS compliance. The grade speaks to the public water system, not the watershed — for watershed-level concerns, see the Watershed Health zone. For the most up-to-date information, contact your local water utility or review your Consumer Confidence Report (CCR).
Why does King County have so many water violations?
King County has 16 health-based drinking water violations on record from the EPA SDWIS database. A higher violation count can result from aging infrastructure, underfunded water utilities, agricultural runoff contamination, or industrial pollution. Counties with more water systems may also see more violations simply due to scale. Residents concerned about water quality should consider independent water testing and home filtration systems.
How does King County rank for water quality in Washington?
King County ranks #11 out of 39 counties in Washington by SDWIS water quality score (1 = best). With a score of 71.1/100, it falls in the top third of counties statewide. The ranking reflects EPA SDWIS compliance only — not watershed impairment, monitoring density, or streamflow, which are tracked separately on this page.

Counties with Similar Water Quality

Clark County

Washington

B

69.5

Water score

Chelan County

Washington

B

68.0

Water score

Kitsap County

Washington

B

67.5

Water score

Data Sources

Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. Scores reflect compliance history and health-based violation counts.

Water-quality monitoring counts from the EPA Water Quality Portal (WQP), federated USGS, EPA, and state agency sampling records over a rolling 5-year window.

Live streamflow from the USGS National Water Information System (NWIS), continuous discharge measurements from the largest-drainage gauge in each county, compared against the full-record long-term annual mean.

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.

By Evan Brooks, Data EditorUpdated Reviewed by Evan Brooks, Data Editor

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