United States Last reviewed: August 28, 2026

Wisconsin Tap Water Quality

Q: Is tap water safe to drink in Wisconsin?

Yes: Milwaukee, Madison, and the major systems meet all standards, with Milwaukee's post-1993 treatment among the most conservative anywhere. Karst-country private wells need frequent testing.

Q: What was the 1993 Milwaukee outbreak?

Cryptosporidium passed through treatment and sickened an estimated 400,000 people: the event that rewrote US surface-water treatment rules and led Milwaukee to add ozone and best-in-class monitoring.

Q: Why did Waukesha switch to Lake Michigan water?

Its deep aquifer wells exceeded radium limits; after a first-of-its-kind approval under the Great Lakes Compact, the city began receiving lake water via Milwaukee in 2023, returning treated wastewater to the basin.

about 1,050

Community water systems

City reports on this site

Tracked contaminants

August 28, 2026

Data reviewed

Check a Wisconsin ZIP Code

Overview

Milwaukee treats Lake Michigan water with ozone and rigorous monitoring, lessons from its 1993 cryptosporidiosis outbreak, the largest waterborne-disease event in US history, and Madison pumps deep, naturally clean aquifer wells. Both comply fully.

Wisconsin's fights are well mapped: lead service lines in Milwaukee and the old industrial cities (a decades-long replacement program), nitrate and bacteria in the karst country of Kewaunee and Door counties where manure reaches wells fast, PFAS in Marinette/Peshtigo (Tyco foam) and La Crosse-area wells, and radium in deep-aquifer systems around Waukesha, which won a precedent-setting Great Lakes diversion to solve it.

Common Contaminants in Wisconsin

Nitrate and bacteria in karst wells

Kewaunee-area fractured bedrock lets manure reach wells rapidly: the state's flagship rural water-justice issue with targeted spreading rules

Lead from service lines

Milwaukee's ~65,000-line inventory anchors a statewide replacement push

PFAS

Marinette/Peshtigo's Tyco foam plume and other sites drove state standards and litigation

Radium

Deep sandstone aquifer systems (Waukesha historically) exceed limits; fixed by treatment or the Lake Michigan diversion

Violations & Compliance

Milwaukee and Madison hold strong records; violations concentrate in karst-country wells (largely private, outside SDWA), small-system radium, and PFAS-affected wells. Waukesha's 2023 switch to lake water resolved the state's most prominent radium case.