waterbycounty
EPA SDWIS

Coles County Water Quality

Coles County, Illinois

Water Grade

B

Water Score

68.4

Violations

1

State Rank

#18

of 102 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

B

Based on EPA compliance history and violation data

Water Score

68.4/100

Higher = better quality

Health Violations

1

Health-based violations

Violation Rate

1.7%

Systems with violations

Water Advisory: Coles County

Water Verdict

Coles County receives a fair water quality assessment with a grade of B and a score of 68.4 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

Coles County has recorded 1 health-based violation, meaning the water system experienced at least one exceedance of federal contaminant limits or treatment requirements. At 1.7 violations per 1,000 residents, this rate is relatively low compared to many U.S. counties.

Consumer Guidance

Tap water in Coles County is generally safe to drink based on available data. Residents should still review their utility's annual Consumer Confidence Report for transparency on detected contaminants. 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

Coles County has better water quality than the average county in Illinois. Its water score is 20.6 points higher than the state average, indicating stronger water system performance relative to neighboring counties.

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

40.7%

332 of 815 assessed

Moderate concern

Top Impairment Causes

  • 1

    PHOSPHORUS, TOTAL

  • 2

    MERCURY

  • 3

    TOTAL SUSPENDED SOLIDS (TSS)

Source: EPA ATTAINS · Reporting cycle 2022

Impairment is determined under the Clean Water Act §303(d): a water body is impaired when it fails to meet state-defined quality standards for designated uses (drinking, recreation, aquatic life). Assessment coverage varies by state — counties without assessed water bodies are not shown.

Past 5 years

Water Quality Monitoring

Monitoring Sites

21

Active in the past 5 years

Measurements Recorded

6.3K

6,266 total readings

Most Measured

  • Physical
  • Inorganics, Minor, Metals
  • Organics, Pesticide

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

353cfs

May 14, 7:00 PM UTC

vs Long-Term Average

79%

Below typical

Primary Streamgage

KASKASKIA RIVER AT COOKS MILLS, IL

USGS site
05591200
Drainage area
473 sq mi
Long-term mean
448 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 Coles County, Illinois?
Coles County, Illinois has a drinking-water quality grade of B with a score of 68.4/100, 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 Coles County?
Coles 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 healthy are the watersheds in Coles County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 40.7% of Coles County's 815 assessed water bodies are classified as impaired (332 impaired). The top reported causes are PHOSPHORUS, TOTAL, MERCURY, TOTAL SUSPENDED SOLIDS (TSS). Impairment means the water body fails to meet state quality standards for at least one designated use — drinking water source, recreation, aquatic life, or fish consumption. Note: watershed impairment doesn't always translate to tap-water issues; treatment plants can remove most regulated contaminants.
How much water-quality monitoring happens in Coles County?
EPA's Water Quality Portal records 6,266 measurements from 21 monitoring sites in Coles County over the past five years. The most frequently measured characteristic groups are Physical, Inorganics, Minor, Metals, Organics, Pesticide. 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 Coles County right now?
Coles County's primary USGS streamgage on the KASKASKIA RIVER is currently reading 353 cubic feet per second — 79% of the long-term mean of 448.04 cfs. Flow is within typical range for this gauge. For genuine real-time data, visit waterdata.usgs.gov.
How does Coles County water compare to the Illinois average?
Coles County's SDWIS water quality score of 68.4/100 is higher than the Illinois state average of 47.8. The average water quality grade across Illinois is D, based on data from 102 counties with available SDWIS data.
Is tap water safe to drink in Coles County?
Based on EPA SDWIS data, Coles County has a water quality grade of B (68.4/100). 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).
Does Coles County have clean drinking water?
Coles County has 1 health-based drinking water violation according to EPA records. With a water quality score of 68.4/100 and grade B, 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 Coles County rank for water quality in Illinois?
Coles County ranks #18 out of 102 counties in Illinois by SDWIS water quality score (1 = best). With a score of 68.4/100, 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

Peoria County

Illinois

B

68.2

Water score

Kendall County

Illinois

B

69.3

Water score

Franklin County

Illinois

B

67.1

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.

Watershed health and impaired-waterway data from the EPA ATTAINS Clean Water Act §303(d) assessments — state-reported, EPA-finalized.

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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