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County water report

Coles County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for Coles County, Illinois.

Water grade

B

Water score

68.4

State rank

#18

of 102

Health violations

1

EPA SDWIS, 5-year lookback

Watershed impaired

40.7%

815 water bodies assessed

Monitoring sites

21

6,266 recent measurements

Live streamflow

79%

KASKASKIA RIVER AT COOKS MILLS, IL

Water at a glance

Key Water Indicators for Coles County

EPA SDWIS

Safety Grade

B

Score: 68.4 / 100

EPA SDWIS

Active Violations

1

5-year health-based lookback

EPA ATTAINS

Watershed Health

41% impaired

815 bodies assessed

USGS NWIS

Streamflow Snapshot

79% of mean

KASKASKIA RIVER AT COOKS MILLS, IL

EPA WQP

Monitoring Sites

21

6,266 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

B

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

68.4/100

Health violations

1

Health-based violations

Violations per 100K served

1.7

Population-normalized SDWIS rate

Editorial analysis

Understanding Coles County’s Water

Drinking Water Quality Overview

EPA SDWIS

Coles County earns a B grade for drinking water quality, scoring 68.4 out of 100. Over the past five years, EPA SDWIS records 1 health-based violation — a single incident worth monitoring.

Watershed Conditions

EPA ATTAINS

Under the Clean Water Act §303(d), EPA ATTAINS tracks whether waterways meet quality standards for drinking, recreation, and aquatic life (reporting cycle: 2022). A substantial 40.7% of assessed waterways are impaired (332 of 815 water bodies) across Coles County's watersheds. The leading impairment causes are phosphorus, total and mercury. Impairment does not mean tap water is unsafe — it measures ambient waterway conditions upstream of treatment, not finished drinking water.

River & Streamflow Status

USGS NWIS

USGS NWIS gauge data (as of 2026-05-14T13:00:00.000-06:00) puts KASKASKIA RIVER at 353.0 cfs — running somewhat below its historical average at 79% of mean. 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. Coles County has moderate coverage with 21 active monitoring sites with 6,266 recent measurements on record. Predominant monitoring categories include physical and inorganics, minor, metals. 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 Coles County

Water Verdict

Coles County, Illinois 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. Separately, EPA ATTAINS assessments cover 815 water bodies in the county's watershed, with 40.7% listed as impaired under the Clean Water Act — a source-water measure that is tracked independently of tap-water compliance. At the most recent USGS reading, local streamflow was below its historical mean at 78.8% — worth watching in drier seasons.

Violation Context

EPA SDWIS records for Coles County, Illinois show 1 health-based violation, meaning a water system experienced at least one exceedance of federal contaminant limits or treatment requirements. At 1.7 violations per 100,000 people served, this rate is relatively low compared to many U.S. counties. For independent context, 6,266 water-quality monitoring results have been recorded across the county in the EPA Water Quality Portal over the past five years.

Consumer Guidance

Tap water in Coles County scores well above average for drinking-water safety. Coles County's drinking-water compliance score is 68.4 out of 100. With 1 recorded health violation, the water supply is generally reliable. The violation rate for Coles County is 1.7 per 100,000 people served. Households with infants, pregnant individuals, or immunocompromised members may want to use an NSF 53-certified pitcher filter as a low-cost precaution. Phosphorus, Total is the leading impairment cause in Coles County's watershed. With 21 active water-quality monitoring sites in Coles County, data coverage is strong. A pipeline streamflow snapshot from the KASKASKIA RIVER gauge is also available on this page.

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.

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 Coles County's water environment

Watershed Impairment Causes (EPA ATTAINS)

  • 1

    Phosphorus (excess nutrients)

    Impairment cause per EPA Clean Water Act §303(d) assessment

  • 2

    Mercury

    Impairment cause per EPA Clean Water Act §303(d) assessment

  • 3

    Total Suspended Solids (Tss)

    Impairment cause per EPA Clean Water Act §303(d) assessment

Source: EPA ATTAINS · Reporting cycle 2022

Official EPA Resources for Coles County

EPA How's My Waterway

Interactive watershed health data for Coles County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Coles County

Consumer Confidence Reports (IL)

Annual water quality reports from utilities in Illinois

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; 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 Coles 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.

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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 streamflow snapshots 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 has a pipeline snapshot of 353 cubic feet per second — 79% of the long-term mean of 448.04 cfs. Flow is within typical range for this gauge. For the latest gauge feed, 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 and 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 Evan Brooks, Data EditorUpdated Reviewed by Evan Brooks, Data Editor

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