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County water report

Johnson County Water Report

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

Water grade

F

Water score

15.8

State rank

#96

of 102

Health violations

15

EPA SDWIS, 5-year lookback

Watershed impaired

38.3%

167 water bodies assessed

Monitoring sites

6

1,370 recent measurements

Live streamflow

1%

CACHE RIVER AT FORMAN, IL

Water at a glance

Key Water Indicators for Johnson County

EPA SDWIS

Safety Grade

F

Score: 15.8 / 100

EPA SDWIS

Active Violations

15

5-year health-based lookback

EPA ATTAINS

Watershed Health

38% impaired

167 bodies assessed

USGS NWIS

Streamflow Snapshot

1% of mean

CACHE RIVER AT FORMAN, IL

EPA WQP

Monitoring Sites

6

1,370 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

F

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

15.8/100

Health violations

15

Health-based violations

Violations per 100K served

187.0

Population-normalized SDWIS rate

Editorial analysis

Understanding Johnson County’s Water

Drinking Water Quality Overview

EPA SDWIS

Johnson County's water systems carry a failing grade, scoring 15.8 out of 100. Over the past five years, EPA SDWIS records 15 health-based violations — a pattern that public water utilities are required to disclose and correct.

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 38.3% of assessed waterways are impaired (64 of 167 water bodies) across Johnson County's watersheds. The leading impairment causes are mercury and dissolved oxygen. 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 CACHE RIVER at 3.4 cfs — well below its long-term average at 1% 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. Johnson County has limited coverage with 6 active monitoring sites with 1,370 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 Johnson County

Water Verdict

Johnson County, Illinois receives a poor water quality assessment with a grade of F and a score of 15.8 out of 100. The water supply has documented quality issues. Residents are strongly encouraged to use filtered or bottled water for drinking and to stay informed about utility improvement plans. Separately, EPA ATTAINS assessments cover 167 water bodies in the county's watershed, with 38.3% 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 1.1% — worth watching in drier seasons.

Violation Context

EPA SDWIS records for Johnson County, Illinois show 15 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 187.0 violations per 100,000 people served, this rate is high and signals significant water quality management issues. For independent context, 1,370 water-quality monitoring results have been recorded across the county in the EPA Water Quality Portal over the past five years.

Consumer Guidance

Drinking-water compliance in Johnson County is rated Grade F, reflecting significant health-based violations in the recent reporting period. Johnson County's drinking-water compliance score is 15.8 out of 100. An NSF 53 or NSF 58-certified filter is recommended for drinking and cooking water. Check the Consumer Confidence Report from your utility to identify the specific contaminants and required corrective actions — utilities are legally required to notify customers of violations. Mercury is the leading impairment cause in Johnson County's watershed. There are 6 active water-quality monitoring sites in Johnson County. A pipeline streamflow snapshot from the CACHE RIVER gauge is also available on this page.

Regional Context

Johnson County has poorer water quality than the average county in Illinois. Its water score is 32 points lower than the state average, suggesting more challenges with contamination control or infrastructure than 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 Johnson County's water environment

Watershed Impairment Causes (EPA ATTAINS)

  • 1

    Mercury

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

  • 2

    Low dissolved oxygen

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

  • 3

    Alteration in Stream-Side Or Littoral Vegetative Covers

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

Source: EPA ATTAINS · Reporting cycle 2022

Official EPA Resources for Johnson County

EPA How's My Waterway

Interactive watershed health data for Johnson County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Johnson County

Consumer Confidence Reports (IL)

Annual water quality reports from utilities in Illinois

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

38.3%

64 of 167 assessed

Moderate concern

Top Impairment Causes

  • 1

    MERCURY

  • 2

    DISSOLVED OXYGEN

  • 3

    ALTERATION IN STREAM-SIDE OR LITTORAL VEGETATIVE COVERS

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

6

Active in the past 5 years

Measurements Recorded

1.4K

1,370 total readings

Most Measured

  • Physical
  • Inorganics, Minor, Metals
  • Not Assigned

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

3.41cfs

May 14, 7:00 PM UTC

vs Long-Term Average

1%

Well below typical

Primary Streamgage

CACHE RIVER AT FORMAN, IL

USGS site
03612000
Drainage area
244 sq mi
Long-term mean
316 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 Johnson 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 Johnson County, Illinois?
Johnson County, Illinois has a drinking-water quality grade of F with a score of 15.8/100, based on EPA SDWIS compliance data. The county has 15 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and streamflow snapshots are reported separately on this page.
Are there any water violations in Johnson County?
Johnson County has 15 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 healthy are the watersheds in Johnson County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 38.3% of Johnson County's 167 assessed water bodies are classified as impaired (64 impaired). The top reported causes are MERCURY, DISSOLVED OXYGEN, ALTERATION IN STREAM-SIDE OR LITTORAL VEGETATIVE COVERS. 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 Johnson County?
EPA's Water Quality Portal records 1,370 measurements from 6 monitoring sites in Johnson County over the past five years. The most frequently measured characteristic groups are Physical, Inorganics, Minor, Metals, Not Assigned. 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 Johnson County right now?
Johnson County's primary USGS streamgage on the CACHE RIVER has a pipeline snapshot of 3.41 cubic feet per second — 1% of the long-term mean of 315.93 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 Johnson County water compare to the Illinois average?
Johnson County's SDWIS water quality score of 15.8/100 is lower 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 Johnson County?
Based on EPA SDWIS data, Johnson County has a water quality grade of F (15.8/100). This indicates below-average compliance with significant violations. Residents may want to consider home water filtration or independent testing. 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 Johnson County have so many water violations?
Johnson County has 15 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 Johnson County rank for water quality in Illinois?
Johnson County ranks #96 out of 102 counties in Illinois by SDWIS water quality score (1 = best). With a score of 15.8/100, 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

Wayne County

Illinois

F

15.4

Water score

LaSalle County

Illinois

F

15.3

Water score

Macoupin County

Illinois

F

16.5

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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