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EPA SDWIS

Thurston County Water Quality

Thurston County, Washington

Water Grade

C

Water Score

50.8

Violations

55

State Rank

#29

of 39 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

C

Based on EPA compliance history and violation data

Water Score

50.8/100

Higher = better quality

Health Violations

55

Health-based violations

Violation Rate

15.0%

Systems with violations

Water Advisory: Thurston County

Water Verdict

Thurston County receives a below-average water quality assessment with a grade of C and a score of 50.8 out of 100. Residents should review their utility's Consumer Confidence Report and may want to consider additional water filtration for drinking.

Violation Context

Thurston County has recorded 55 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 15.0 violations per 1,000 residents, this rate is high and signals significant water quality management issues.

Consumer Guidance

Tap water in Thurston County meets baseline standards, but residents who are immunocompromised or have young children may want to use an NSF-certified water filter as a precaution. With 55 recorded health violations, staying informed about utility communications and boil-water notices is especially important. For long-term peace of mind, request your utility's latest Consumer Confidence Report and consider independent water testing if you have specific health concerns.

Regional Context

Thurston County has poorer water quality than the average county in Washington. Its water score is 8.5 points lower than the state average, suggesting more challenges with contamination control or infrastructure than neighboring counties.

Past 5 years

Water Quality Monitoring

Monitoring Sites

838

Active in the past 5 years

Measurements Recorded

100K

100,252 total readings

Most Measured

  • Physical
  • Organics, Other
  • Microbiological

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

727cfs

May 14, 7:00 PM UTC

vs Long-Term Average

26%

Well below typical

Primary Streamgage

CHEHALIS RIVER NEAR GRAND MOUND, WA

USGS site
12027500
Drainage area
895 sq mi
Long-term mean
2,829 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; "% of typical" compares the latest reading against that average.

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Frequently Asked Questions

What is the water quality in Thurston County, Washington?
Thurston County, Washington has a drinking-water quality grade of C with a score of 50.8/100, based on EPA SDWIS compliance data. The county has 55 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and live streamflow are reported separately on this page.
Are there any water violations in Thurston County?
Thurston County has 55 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 Thurston County?
EPA's Water Quality Portal records 100,252 measurements from 838 monitoring sites in Thurston County over the past five years. The most frequently measured characteristic groups are Physical, Organics, Other, Microbiological. 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 Thurston County right now?
Thurston County's primary USGS streamgage on the CHEHALIS RIVER is currently reading 727 cubic feet per second — 26% of the long-term mean of 2,829.34 cfs. This is well below typical — often a signal of drought stress on source water. For genuine real-time data, visit waterdata.usgs.gov.
How does Thurston County water compare to the Washington average?
Thurston County's SDWIS water quality score of 50.8/100 is lower 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 Thurston County?
Based on EPA SDWIS data, Thurston County has a water quality grade of C (50.8/100). This indicates moderate compliance. Some violations have been recorded but overall standards are maintained. 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 Thurston County have so many water violations?
Thurston County has 55 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 Thurston County rank for water quality in Washington?
Thurston County ranks #29 out of 39 counties in Washington by SDWIS water quality score (1 = best). With a score of 50.8/100, it falls in the bottom 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

Lewis County

Washington

D

49.9

Water score

Okanogan County

Washington

D

49.7

Water score

Walla Walla County

Washington

C

53.3

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 Logan Johnson, Founder & Data EditorUpdated Reviewed by Logan Johnson, Founder & Data Editor

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