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Federal water data

County water report

Rock County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for Rock County, Wisconsin.

Water grade

C

Water score

57.1

State rank

#14

of 71

Health violations

11

EPA SDWIS, 5-year lookback

Watershed impaired

12.1%

257 water bodies assessed

Monitoring sites

118

53,282 recent measurements

Live streamflow

238%

ROCK RIVER AT AFTON, WI

Water at a glance

Key Water Indicators for Rock County

EPA SDWIS

Safety Grade

C

Score: 57.1 / 100

EPA SDWIS

Active Violations

11

5-year health-based lookback

EPA ATTAINS

Watershed Health

12% impaired

257 bodies assessed

USGS NWIS

Streamflow Snapshot

238% of mean

ROCK RIVER AT AFTON, WI

EPA WQP

Monitoring Sites

118

53,282 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

11

Health-based violations

Violations per 100K served

8.8

Population-normalized SDWIS rate

Editorial analysis

Understanding Rock County’s Water

Drinking Water Quality Overview

EPA SDWIS

Rock County's drinking water earned a C grade, scoring 57.1 out of 100. Over the past five years, EPA SDWIS records 11 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 notable 12.1% of assessed waterways carry an impairment designation (31 of 257 water bodies) across Rock County's watersheds. The leading impairment causes are phosphorus, total and total suspended solids (tss). 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 2026-05-14T14:00:00.000-05:00) puts ROCK RIVER at 5.1k cfs — running significantly above its long-term average at 238% 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. Rock County has extensive coverage with 118 active monitoring sites with 53,282 recent measurements on record. Predominant monitoring categories include physical and organics, pesticide. 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 Rock County

Water Verdict

Rock County, Wisconsin 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 257 water bodies in the county's watershed, with 12.1% 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 237.5%.

Violation Context

EPA SDWIS records for Rock County, Wisconsin show 11 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 8.8 violations per 100,000 people served, this rate is high and signals significant water quality management issues. This compliance record sits alongside an unusually deep monitoring archive: 53,282 water-quality results have been logged across the county in the EPA Water Quality Portal over the past five years.

Consumer Guidance

Tap water in Rock County meets baseline standards but the compliance record shows room for improvement, with a Grade C rating. Rock County's drinking-water compliance score is 57.1 out of 100. The violation rate for Rock County is 8.8 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. Phosphorus, Total is the leading impairment cause in Rock County's watershed. With 118 active water-quality monitoring sites in Rock County, data coverage is strong. A pipeline streamflow snapshot from the ROCK RIVER gauge is also available on this page.

Regional Context

Rock County has better water quality than the average county in Wisconsin. Its water score is 17.6 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 Rock County's water environment

Watershed Impairment Causes (EPA ATTAINS)

  • 1

    Phosphorus (excess nutrients)

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

  • 2

    Total Suspended Solids (Tss)

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

  • 3

    E. coli (bacteria)

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

Source: EPA ATTAINS · Reporting cycle 2022

Official EPA Resources for Rock County

EPA How's My Waterway

Interactive watershed health data for Rock County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Rock County

Consumer Confidence Reports (WI)

Annual water quality reports from utilities in Wisconsin

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

12.1%

31 of 257 assessed

Some impairment

Top Impairment Causes

  • 1

    PHOSPHORUS, TOTAL

  • 2

    TOTAL SUSPENDED SOLIDS (TSS)

  • 3

    ESCHERICHIA COLI (E. COLI)

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

118

Active in the past 5 years

Measurements Recorded

53K

53,282 total readings

Most Measured

  • Physical
  • Organics, Pesticide
  • Nutrient

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

5,080cfs

May 14, 7:00 PM UTC

vs Long-Term Average

238%

Well above typical

Primary Streamgage

ROCK RIVER AT AFTON, WI

USGS site
05430500
Drainage area
3,340 sq mi
Long-term mean
2,139 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.

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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 Rock 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 Rock County, Wisconsin?
Rock County, Wisconsin has a drinking-water quality grade of C with a score of 57.1/100, based on EPA SDWIS compliance data. The county has 11 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 Rock County?
Rock County has 11 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 Rock County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 12.1% of Rock County's 257 assessed water bodies are classified as impaired (31 impaired). The top reported causes are PHOSPHORUS, TOTAL, TOTAL SUSPENDED SOLIDS (TSS), ESCHERICHIA COLI (E. COLI). 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 Rock County?
EPA's Water Quality Portal records 53,282 measurements from 118 monitoring sites in Rock County over the past five years. The most frequently measured characteristic groups are Physical, Organics, Pesticide, Nutrient. 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 Rock County right now?
Rock County's primary USGS streamgage on the ROCK RIVER has a pipeline snapshot of 5,080 cubic feet per second — 238% of the long-term mean of 2,138.55 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 Rock County water compare to the Wisconsin average?
Rock County's SDWIS water quality score of 57.1/100 is higher than the Wisconsin state average of 39.5. The average water quality grade across Wisconsin is F, based on data from 71 counties with available SDWIS data.
Is tap water safe to drink in Rock County?
Based on EPA SDWIS data, Rock 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 Rock County have so many water violations?
Rock County has 11 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 Rock County rank for water quality in Wisconsin?
Rock County ranks #14 out of 71 counties in Wisconsin by SDWIS water quality score (1 = best). With a score of 57.1/100, 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

Waupaca County

Wisconsin

C

58.1

Water score

Chippewa County

Wisconsin

C

56.0

Water score

Fond du Lac County

Wisconsin

C

60.4

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 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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