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County water report

Winnebago County Water Report

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

Water grade

C

Water score

57.1

State rank

#37

of 102

Health violations

21

EPA SDWIS, 5-year lookback

Watershed impaired

43.9%

346 water bodies assessed

Monitoring sites

17

3,633 recent measurements

Live streamflow

161%

ROCK RIVER AT ROCKTON, IL

Water at a glance

Key Water Indicators for Winnebago County

EPA SDWIS

Safety Grade

C

Score: 57.1 / 100

EPA SDWIS

Active Violations

21

5-year health-based lookback

EPA ATTAINS

Watershed Health

44% impaired

346 bodies assessed

USGS NWIS

Streamflow Snapshot

161% of mean

ROCK RIVER AT ROCKTON, IL

EPA WQP

Monitoring Sites

17

3,633 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.

57.1/100

Health violations

21

Health-based violations

Violations per 100K served

8.7

Population-normalized SDWIS rate

Editorial analysis

Understanding Winnebago County’s Water

Drinking Water Quality Overview

EPA SDWIS

Winnebago County's drinking water earned a C grade, scoring 57.1 out of 100. Over the past five years, EPA SDWIS records 21 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 43.9% of assessed waterways are impaired (152 of 346 water bodies) across Winnebago County's watersheds. The leading impairment causes are mercury and polychlorinated biphenyls (pcbs). 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 2026-05-14T12:30:00.000-06:00) puts ROCK RIVER at 7.6k cfs — running significantly above its long-term average at 161% of mean flow. 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. Winnebago County has moderate coverage with 17 active monitoring sites with 3,633 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 Winnebago County

Water Verdict

Winnebago County, Illinois receives a fair water quality assessment with a grade of C and a score of 57.1 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 346 water bodies in the county's watershed, with 43.9% 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 running above its historical mean at 160.9%.

Violation Context

EPA SDWIS records for Winnebago County, Illinois show 21 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 8.7 violations per 100,000 people served, this rate is high and signals significant water quality management issues. For independent context, 3,633 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 Winnebago County meets baseline standards but the compliance record shows room for improvement, with a Grade C rating. Winnebago County's drinking-water compliance score is 57.1 out of 100. The violation rate for Winnebago County is 8.7 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. Mercury is the leading impairment cause in Winnebago County's watershed. With 17 active water-quality monitoring sites in Winnebago County, data coverage is strong. A pipeline streamflow snapshot from the ROCK RIVER gauge is also available on this page.

Regional Context

Winnebago County has better water quality than the average county in Illinois. Its water score is 9.3 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 Winnebago County's water environment

Watershed Impairment Causes (EPA ATTAINS)

  • 1

    Mercury

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

  • 2

    Polychlorinated Biphenyls (Pcbs)

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

  • 3

    Cause Unknown

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

Source: EPA ATTAINS · Reporting cycle 2022

Official EPA Resources for Winnebago County

EPA How's My Waterway

Interactive watershed health data for Winnebago County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Winnebago County

Consumer Confidence Reports (IL)

Annual water quality reports from utilities in Illinois

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

43.9%

152 of 346 assessed

Moderate concern

Top Impairment Causes

  • 1

    MERCURY

  • 2

    POLYCHLORINATED BIPHENYLS (PCBS)

  • 3

    CAUSE UNKNOWN

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

17

Active in the past 5 years

Measurements Recorded

3.6K

3,633 total readings

Most Measured

  • Physical
  • Inorganics, Minor, Metals
  • 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

7,640cfs

May 14, 6:30 PM UTC

vs Long-Term Average

161%

Well above typical

Primary Streamgage

ROCK RIVER AT ROCKTON, IL

USGS site
05437500
Drainage area
6,363 sq mi
Long-term mean
4,748 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 Winnebago 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 Winnebago County, Illinois?
Winnebago County, Illinois has a drinking-water quality grade of C with a score of 57.1/100, based on EPA SDWIS compliance data. The county has 21 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 Winnebago County?
Winnebago County has 21 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 Winnebago County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 43.9% of Winnebago County's 346 assessed water bodies are classified as impaired (152 impaired). The top reported causes are MERCURY, POLYCHLORINATED BIPHENYLS (PCBS), CAUSE UNKNOWN. 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 Winnebago County?
EPA's Water Quality Portal records 3,633 measurements from 17 monitoring sites in Winnebago County over the past five years. The most frequently measured characteristic groups are Physical, Inorganics, Minor, Metals, 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 Winnebago County right now?
Winnebago County's primary USGS streamgage on the ROCK RIVER has a pipeline snapshot of 7,640 cubic feet per second — 161% of the long-term mean of 4,748.21 cfs. This is well above typical — often a signal of recent precipitation or storm runoff. For the latest gauge feed, visit waterdata.usgs.gov.
How does Winnebago County water compare to the Illinois average?
Winnebago County's SDWIS water quality score of 57.1/100 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 Winnebago County?
Based on EPA SDWIS data, Winnebago County has a water quality grade of C (57.1/100). 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).
Why does Winnebago County have so many water violations?
Winnebago County has 21 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 Winnebago County rank for water quality in Illinois?
Winnebago County ranks #37 out of 102 counties in Illinois by SDWIS water quality score (1 = best). With a score of 57.1/100, 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

De Witt County

Illinois

C

56.9

Water score

Cass County

Illinois

C

56.8

Water score

Lawrence County

Illinois

C

58.3

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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