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Federal water data

County water report

McHenry County Water Report

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

Water grade

B

Water score

67.1

State rank

#21

of 102

Health violations

6

EPA SDWIS, 5-year lookback

Watershed impaired

57.0%

256 water bodies assessed

Monitoring sites

87

14,401 recent measurements

Live streamflow

66%

FOX RIVER (TAILWATER) AT ALGONQUIN, IL

Water at a glance

Key Water Indicators for McHenry County

EPA SDWIS

Safety Grade

B

Score: 67.1 / 100

EPA SDWIS

Active Violations

6

5-year health-based lookback

EPA ATTAINS

Watershed Health

57% impaired

256 bodies assessed

USGS NWIS

Streamflow Snapshot

66% of mean

FOX RIVER (TAILWATER) AT ALGONQUIN, IL

EPA WQP

Monitoring Sites

87

14,401 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.

67.1/100

Health violations

6

Health-based violations

Violations per 100K served

2.4

Population-normalized SDWIS rate

Editorial analysis

Understanding McHenry County’s Water

Drinking Water Quality Overview

EPA SDWIS

McHenry County earns a B grade for drinking water quality, scoring 67.1 out of 100. Over the past five years, EPA SDWIS records 6 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 57.0% of assessed waterways are impaired (146 of 256 water bodies) across McHenry 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 2026-05-14T12:30:00.000-06:00) puts FOX RIVER (TAILWATER) at 883.0 cfs — running somewhat below its historical average at 66% 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. McHenry County has extensive coverage with 87 active monitoring sites with 14,401 recent measurements on record. Predominant monitoring categories include physical and organics, other. 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 McHenry County

Water Verdict

McHenry County receives a fair water quality assessment with a grade of B and a score of 67.1 out of 100. The water supply meets baseline federal standards, but there may be periods of elevated contaminant levels or infrastructure concerns worth monitoring.

Violation Context

McHenry County has recorded 6 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 2.4 violations per 100,000 people served, this rate is relatively low compared to many U.S. counties.

Consumer Guidance

Tap water in McHenry County meets baseline safety standards, though the compliance record shows some violations worth watching. McHenry County's drinking-water compliance score is 67.1 out of 100. The violation rate for McHenry County is 2.4 per 100,000 people served. Running tap water for 30 seconds before drinking can reduce any localized lead exposure from household plumbing. Requesting your utility's most recent Consumer Confidence Report is the fastest way to identify which specific contaminants were flagged. Phosphorus, Total is the leading impairment cause in McHenry County's watershed. With 87 active water-quality monitoring sites in McHenry County, data coverage is strong. A pipeline streamflow snapshot from the FOX RIVER (TAILWATER) gauge is also available on this page.

Regional Context

McHenry County has better water quality than the average county in Illinois. Its water score is 19.3 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 McHenry 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 McHenry County

EPA How's My Waterway

Interactive watershed health data for McHenry County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for McHenry County

Consumer Confidence Reports (IL)

Annual water quality reports from utilities in Illinois

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

57.0%

146 of 256 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

87

Active in the past 5 years

Measurements Recorded

14K

14,401 total readings

Most Measured

  • Physical
  • Organics, Other
  • Inorganics, Minor, 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

883cfs

May 14, 6:30 PM UTC

vs Long-Term Average

66%

Below typical

Primary Streamgage

FOX RIVER (TAILWATER) AT ALGONQUIN, IL

USGS site
05550001
Drainage area
1,429 sq mi
Long-term mean
1,348 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 McHenry 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 McHenry County, Illinois?
McHenry County, Illinois has a drinking-water quality grade of B with a score of 67.1/100, based on EPA SDWIS compliance data. The county has 6 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 McHenry County?
McHenry County has 6 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 McHenry County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 57.0% of McHenry County's 256 assessed water bodies are classified as impaired (146 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 McHenry County?
EPA's Water Quality Portal records 14,401 measurements from 87 monitoring sites in McHenry County over the past five years. The most frequently measured characteristic groups are Physical, Organics, Other, Inorganics, Minor, 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 McHenry County right now?
McHenry County's primary USGS streamgage on the FOX RIVER (TAILWATER) has a pipeline snapshot of 883 cubic feet per second — 66% of the long-term mean of 1,348.34 cfs. Flow is within typical range for this gauge. For the latest gauge feed, visit waterdata.usgs.gov.
How does McHenry County water compare to the Illinois average?
McHenry County's SDWIS water quality score of 67.1/100 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 McHenry County?
Based on EPA SDWIS data, McHenry County has a water quality grade of B (67.1/100). 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).
Why does McHenry County have so many water violations?
McHenry County has 6 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 McHenry County rank for water quality in Illinois?
McHenry County ranks #21 out of 102 counties in Illinois by SDWIS water quality score (1 = best). With a score of 67.1/100, 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

Franklin County

Illinois

B

67.1

Water score

DeKalb County

Illinois

B

66.0

Water score

Peoria County

Illinois

B

68.2

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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