waterbycounty
EPA SDWIS

Clay County Water Quality

Clay County, South Dakota

Water Grade

C

Water Score

57.7

Violations

1

State Rank

#31

of 63 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

C

Based on EPA compliance history and violation data

Water Score

57.7/100

Higher = better quality

Health Violations

1

Health-based violations

Violation Rate

8.4%

Systems with violations

Water Advisory: Clay County

Water Verdict

Clay County receives a fair water quality assessment with a grade of C and a score of 57.7 out of 100. The water supply meets baseline federal standards, but there may be periods of elevated contaminant levels or infrastructure concerns worth monitoring.

Violation Context

Clay County has recorded 1 health-based violation, meaning the water system experienced at least one exceedance of federal contaminant limits or treatment requirements. At 8.4 violations per 1,000 residents, this rate is high and signals significant water quality management issues.

Consumer Guidance

Tap water in Clay 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 1 recorded health violation, 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

Clay County has water quality close to the average county in South Dakota. Its water score is within 0.9 points of the state average, meaning its overall water system performance is broadly representative of South Dakota as a whole.

Past 5 years

Water Quality Monitoring

Monitoring Sites

3

Active in the past 5 years

Measurements Recorded

197

197 total readings

Most Measured

  • Physical
  • Nutrient
  • Inorganics, Major, Metals

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

41.0cfs

May 14, 6:30 PM UTC

vs Long-Term Average

10%

Well below typical

Primary Streamgage

VERMILLION RIVER NEAR VERMILLION,SD

USGS site
06479010
Drainage area
2,254 sq mi
Long-term mean
429 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.

Improve your water quality at home

Berkey filters remove 99.9%+ of contaminants from tap water.

Shop Berkey →

Sponsored

Test your tap water

Tap Score provides professional mail-in water testing.

Get Tested →

Frequently Asked Questions

What is the water quality in Clay County, South Dakota?
Clay County, South Dakota has a drinking-water quality grade of C with a score of 57.7/100, based on EPA SDWIS compliance data. The county has 1 health-based drinking water violation over the past 5 years. Watershed health, monitoring records, and live streamflow are reported separately on this page.
Are there any water violations in Clay County?
Clay County has 1 health-based drinking water violation 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 Clay County?
EPA's Water Quality Portal records 197 measurements from 3 monitoring sites in Clay County over the past five years. The most frequently measured characteristic groups are Physical, Nutrient, Inorganics, Major, Metals. 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 Clay County right now?
Clay County's primary USGS streamgage on the VERMILLION RIVER is currently reading 41 cubic feet per second — 10% of the long-term mean of 428.57 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 Clay County water compare to the South Dakota average?
Clay County's SDWIS water quality score of 57.7/100 is higher than the South Dakota state average of 56.8. The average water quality grade across South Dakota is D, based on data from 63 counties with available SDWIS data.
Is tap water safe to drink in Clay County?
Based on EPA SDWIS data, Clay County has a water quality grade of C (57.7/100). 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).
Does Clay County have clean drinking water?
Clay County has 1 health-based drinking water violation according to EPA records. With a water quality score of 57.7/100 and grade C, the county's drinking water has had some compliance issues but continues to be monitored. Note: drinking-water compliance speaks to the public water system, not necessarily to the watershed itself — check the Watershed Health zone for ATTAINS §303(d) data.
How does Clay County rank for water quality in South Dakota?
Clay County ranks #31 out of 63 counties in South Dakota by SDWIS water quality score (1 = best). With a score of 57.7/100, it falls in the middle 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

Brookings County

South Dakota

C

57.2

Water score

Lincoln County

South Dakota

C

53.2

Water score

Codington County

South Dakota

B

64.1

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

Explore more data for Clay County

Property TaxCost of LivingCrime RateIncomeHealthSchoolsDisaster RiskWeatherCounty Score