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Federal water data

County water report

Clay County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for Clay County, South Dakota.

Water grade

C

Water score

57.7

State rank

#31

of 63

Health violations

1

EPA SDWIS, 5-year lookback

Watershed impaired

Not reported

EPA ATTAINS coverage varies by state

Monitoring sites

3

197 recent measurements

Live streamflow

10%

VERMILLION RIVER NEAR VERMILLION,SD

Water at a glance

Key Water Indicators for Clay County

EPA SDWIS

Safety Grade

C

Score: 57.7 / 100

EPA SDWIS

Active Violations

1

5-year health-based lookback

EPA ATTAINS

Watershed Health

Not reported

Coverage varies by state

USGS NWIS

Streamflow Snapshot

10% of mean

VERMILLION RIVER NEAR VERMILLION,SD

EPA WQP

Monitoring Sites

3

197 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

C

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

57.7/100

Health violations

1

Health-based violations

Violations per 100K served

8.4

Population-normalized SDWIS rate

Editorial analysis

Understanding Clay County’s Water

Drinking Water Quality Overview

EPA SDWIS

Clay County's drinking water earned a C grade, scoring 57.7 out of 100. Over the past five years, EPA SDWIS records 1 health-based violation — a single incident worth monitoring.

River & Streamflow Status

USGS NWIS

USGS NWIS gauge data (as of 2026-05-14T13:30:00.000-05:00) puts VERMILLION RIVER at 41.0 cfs — well below its long-term average at 10% of mean — low-flow conditions worth noting for water-dependent ecosystems. 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. Clay County has limited coverage with 3 active monitoring sites with 197 recent measurements on record. Predominant monitoring categories include physical and nutrient. 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 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 100,000 people served, this rate is high and signals significant water quality management issues.

Consumer Guidance

Tap water in Clay County meets baseline standards but the compliance record shows room for improvement, with a Grade C rating. Clay County's drinking-water compliance score is 57.7 out of 100. The violation rate for Clay County is 8.4 per 100,000 people served. Residents who are immunocompromised, pregnant, or have young children may benefit from using an NSF 53-certified filter. Contacting your local utility for the current Consumer Confidence Report will confirm which specific violations were recorded and whether they have been resolved. There are 3 active water-quality monitoring sites in Clay County. A pipeline streamflow snapshot from the VERMILLION RIVER gauge is also available on this page.

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.

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 Clay County's water environment

Official EPA Resources for Clay County

EPA How's My Waterway

Interactive watershed health data for Clay County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Clay County

Consumer Confidence Reports (SD)

Annual water quality reports from utilities in South Dakota

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; 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 Clay County:D — Poor

Elevated violations or significant watershed impairment.

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.

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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 streamflow snapshots 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 has a pipeline snapshot of 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 the latest gauge feed, 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 Evan Brooks, Data EditorUpdated Reviewed by Evan Brooks, Data Editor

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