waterbycounty
Federal water data

Wisconsin Water Quality

Drinking water data for all 72 counties.

Avg Water Score

39.5

State Grade

F

Counties with Data

71

of 72 total

County water atlas

Wisconsin water signals by county

A state-level 2.5D view across drinking-water compliance, watershed impairment, monitoring density, and streamflow snapshot context. Pin any county, switch layers, then use the lens controls to isolate clean systems, violation clusters, or impaired watersheds without leaving the page.

Counties

72

Avg score

39.5

Watersheds

72

ATTAINS counties

Monitoring

72

56 gauges

State atlas layers combine EPA SDWIS health-based violations, EPA ATTAINS 303(d) impairment assessments, EPA Water Quality Portal monitoring sites, and representative USGS NWIS streamflow gauges. Streamflow values are pipeline snapshots, not a real-time stream. County pages include the source-specific detail behind each layer.

Multi-source coverage in Wisconsin

Beyond Drinking Water

EPA SDWIS

71/ 72

counties with drinking-water compliance data

1,065 health violations statewide (5yr)

EPA ATTAINS

7.6%

avg impaired across 72 counties

1,993 of 37,217 assessed bodies impaired

EPA WQP

7,751

monitoring sites across 72 counties

5,139,470 total readings (5yr window)

USGS NWIS

56

counties with an active streamgage

15 above28 below

State atlas notes

What stands out in Wisconsin

County water quality is not one number. The strongest read comes from comparing drinking-water compliance against watershed impairment, monitoring density, and streamflow context. Use these signals as a starting point, then open any county profile for source-level detail.

Compliance spread

Door County leads the state score table at 86.0/100, while Adams County sits at 3.7/100. That is a 82.3 point gap inside one state.

Zero health violations

1

3+ health violations

60

Watershed pressure

The atlas impairment layer points to counties where assessed water bodies are most likely to miss state quality standards. Assessment density varies, so compare the percentage with the number of assessed bodies on the county page.

Milwaukee County28.9%Calumet County25.0%Pepin County18.8%

Monitoring hubs

Milwaukee County515 sitesDane County362 sitesBrown County346 sites

Lowest flow reads

Walworth County0%Clark County31%Jackson County40%

Highest current streamflow readings: Brown County (251%), Fond du Lac County (248%), Rock County (238%). High flow can reflect recent storms or runoff, not necessarily safer source water.

All Wisconsin Counties

CountyWater Score
Door County86.0
Milwaukee County71.5
Wood County67.5
Portage County67.3
Outagamie County66.2
Dane County65.0
Racine County63.2
Washington County63.2
Brown County62.3
La Crosse County61.5
Sheboygan County61.2
Fond du Lac County60.4
Waupaca County58.1
Rock County57.1
Chippewa County56.0
St. Croix County53.8
Eau Claire County53.6
Manitowoc County51.8
Marathon County50.7
Kenosha County49.0
Dunn County48.2
Pierce County48.2
Winnebago County47.9
Green Lake County46.4
Lincoln County46.0
Kewaunee County45.9
Calumet County45.5
Ozaukee County45.2
Barron County45.1
Sauk County44.4
Shawano County44.3
Polk County44.0
Walworth County42.7
Burnett County41.8
Waushara County40.3
Juneau County39.7
Green County39.1
Monroe County37.3
Buffalo County36.7
Oneida County36.6
Bayfield County34.3
Marinette County33.3
Douglas County33.2
Price County32.8
Richland County32.2
Dodge County31.9
Oconto County31.7
Washburn County31.1
Jackson County30.3
Trempealeau County29.1
Jefferson County28.7
Grant County27.9
Langlade County24.3
Lafayette County23.2
Columbia County22.3
Clark County22.0
Vernon County22.0
Crawford County21.1
Taylor County20.6
Vilas County20.6
Forest County20.5
Marquette County20.0
Waukesha County19.5
Iron County19.1
Sawyer County17.9
Iowa County17.1
Pepin County12.4
Rusk County12.0
Florence County10.6
Ashland County9.5
Adams County3.7
Menominee County—

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Frequently Asked Questions

Which county in Wisconsin has the best water quality?
Door County has the highest SDWIS water quality score in Wisconsin at 86.0/100 (Grade: A). Note: this ranking reflects drinking-water compliance only — watershed health, monitoring density, and streamflow are tracked separately on each county page.
Which county in Wisconsin has the most water violations?
Adams County has among the lowest SDWIS water quality scores in Wisconsin at 3.7/100. See the individual county page for detailed violation history, watershed assessments, monitoring records, and streamflow data.
How healthy are Wisconsin's watersheds?
Across the 72 Wisconsin counties with EPA ATTAINS §303(d) assessments, an average of 7.6% of assessed water bodies are classified as impaired — 1,993 of 37,217 reported assessments. Impairment is a Clean Water Act designation that a water body fails to meet state quality standards for one or more designated uses.
What are streams and rivers doing across Wisconsin right now?
Of the 56 Wisconsin counties with an active USGS streamgage, 15 are currently flowing above their long-term mean and 28 are flowing below. Above-typical can indicate recent storm runoff; below-typical can indicate drought stress on source water. See each county page for the specific gauge and reading.
Is the tap water safe to drink in Wisconsin?
Wisconsin has an average SDWIS water quality score of 39.5/100 across counties with reporting. Individual county scores vary — check your specific county's page for compliance, watershed health, monitoring records, and streamflow snapshots.
What contaminants are tracked in Wisconsin water supplies?
EPA SDWIS tracks violations for regulated contaminants like lead, nitrates, bacteria, disinfection byproducts, and others. EPA ATTAINS captures broader watershed impairments including mercury, E. coli, sediment, nutrients, and PCBs. The Water Quality Portal aggregates monitoring records from federal, state, and tribal sources. See individual county pages for source-specific detail.
What's the difference between SDWIS, ATTAINS, WQP, and NWIS?
Each one measures a different layer of water. EPA SDWIS tracks drinking-water compliance — whether your public water system met federal Safe Drinking Water Act standards. EPA ATTAINS records §303(d) assessments — what share of a county's rivers, lakes, and streams fail state quality standards under the Clean Water Act. EPA WQP aggregates monitoring records — how many samples have been taken and what's being measured. USGS NWIS provides streamflow snapshots — how much water was flowing through the county's primary streamgage when the pipeline last ran. SDWIS speaks to your tap; the other three speak to source water and the watershed.
What does it mean when a water body is impaired?
An 'impaired' designation under Clean Water Act §303(d) means the state has determined the water body fails to meet its designated-use quality standards — drinking water source, recreation, aquatic life, or fish consumption — for one or more pollutants. Top causes nationally include mercury, E. coli (and other fecal indicator bacteria), nutrients, sediment, and PCBs. Impairment is a structural signal about the watershed, not necessarily about what comes out of your tap (treatment plants can remove or reduce contaminants before delivery).

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.

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.

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