waterbycounty
EPA SDWIS

Hamilton County Water Quality

Hamilton County, Illinois

Water Grade

C

Water Score

52.8

Violations

1

State Rank

#45

of 102 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

C

Based on EPA compliance history and violation data

Water Score

52.8/100

Higher = better quality

Health Violations

1

Health-based violations

Violation Rate

12.7%

Systems with violations

Water Advisory: Hamilton County

Water Verdict

Hamilton County receives a below-average water quality assessment with a grade of C and a score of 52.8 out of 100. Residents should review their utility's Consumer Confidence Report and may want to consider additional water filtration for drinking.

Violation Context

Hamilton County has recorded 1 health-based violation, meaning the water system experienced at least one exceedance of federal contaminant limits or treatment requirements. At 12.7 violations per 1,000 residents, this rate is high and signals significant water quality management issues.

Consumer Guidance

Tap water in Hamilton County meets baseline standards, but residents who are immunocompromised or have young children may want to use an NSF-certified water filter as a precaution. 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

Hamilton County has better water quality than the average county in Illinois. Its water score is 5 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

52.5%

62 of 118 assessed

Moderate concern

Top Impairment Causes

  • 1

    ALTERATION IN STREAM-SIDE OR LITTORAL VEGETATIVE COVERS

  • 2

    DISSOLVED OXYGEN

  • 3

    LOSS OF INSTREAM COVER

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

2

Active in the past 5 years

Measurements Recorded

378

378 total readings

Most Measured

  • Inorganics, Minor, Metals
  • Physical
  • 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).

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Frequently Asked Questions

What is the water quality in Hamilton County, Illinois?
Hamilton County, Illinois has a drinking-water quality grade of C with a score of 52.8/100, 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 Hamilton County?
Hamilton 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 Hamilton County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 52.5% of Hamilton County's 118 assessed water bodies are classified as impaired (62 impaired). The top reported causes are ALTERATION IN STREAM-SIDE OR LITTORAL VEGETATIVE COVERS, DISSOLVED OXYGEN, LOSS OF INSTREAM COVER. 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 Hamilton County?
EPA's Water Quality Portal records 378 measurements from 2 monitoring sites in Hamilton County over the past five years. The most frequently measured characteristic groups are Inorganics, Minor, Metals, Physical, 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.
How does Hamilton County water compare to the Illinois average?
Hamilton County's SDWIS water quality score of 52.8/100 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 Hamilton County?
Based on EPA SDWIS data, Hamilton County has a water quality grade of C (52.8/100). 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 Hamilton County have clean drinking water?
Hamilton County has 1 health-based drinking water violation according to EPA records. With a water quality score of 52.8/100 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 Hamilton County rank for water quality in Illinois?
Hamilton County ranks #45 out of 102 counties in Illinois by SDWIS water quality score (1 = best). With a score of 52.8/100, 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

Rock Island County

Illinois

C

53.1

Water score

Whiteside County

Illinois

C

52.3

Water score

Knox County

Illinois

C

54.4

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.

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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