We analyzed tap water quality data for hundreds of cities in Wisconsin to identify the 25 with the most contaminants exceeding health guidelines. This ranking is based on 2026 data from the EPA and EWG databases.
While all public water systems must meet EPA legal limits, many health experts — including the Environmental Working Group — argue that these legal limits are outdated and don't reflect current scientific understanding of safe exposure levels. The cities below have the widest gap between what's in their water and what's considered safe by modern health standards.
Rankings at a Glance
Marshfield, Wisconsin
Marshfield has 24 contaminants exceeding EWG health guidelines out of 39 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Marshfield water report →Weston, Wisconsin
Weston has 21 contaminants exceeding EWG health guidelines out of 37 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Weston water report →Madison, Wisconsin
Madison has 20 contaminants exceeding EWG health guidelines out of 54 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Madison water report →La Crosse, Wisconsin
La Crosse has 20 contaminants exceeding EWG health guidelines out of 44 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full La Crosse water report →Manitowoc, Wisconsin
Manitowoc has 20 contaminants exceeding EWG health guidelines out of 35 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Manitowoc water report →Bellevue, Wisconsin
Bellevue has 20 contaminants exceeding EWG health guidelines out of 35 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Bellevue water report →Saukville, Wisconsin
Saukville has 19 contaminants exceeding EWG health guidelines out of 32 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Saukville water report →Hobart, Wisconsin
Hobart has 18 contaminants exceeding EWG health guidelines out of 37 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Hobart water report →Green Bay, Wisconsin
Green Bay has 18 contaminants exceeding EWG health guidelines out of 36 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Green Bay water report →New Franken, Wisconsin
New Franken has 18 contaminants exceeding EWG health guidelines out of 36 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full New Franken water report →Bristol, Wisconsin
Bristol has 18 contaminants exceeding EWG health guidelines out of 35 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Bristol water report →Waukesha, Wisconsin
Waukesha has 18 contaminants exceeding EWG health guidelines out of 34 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Waukesha water report →Onalaska, Wisconsin
Onalaska has 18 contaminants exceeding EWG health guidelines out of 34 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Onalaska water report →Oak Creek, Wisconsin
Oak Creek has 18 contaminants exceeding EWG health guidelines out of 33 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Oak Creek water report →Racine, Wisconsin
Racine has 18 contaminants exceeding EWG health guidelines out of 32 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Racine water report →Oshkosh, Wisconsin
Oshkosh has 18 contaminants exceeding EWG health guidelines out of 32 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Oshkosh water report →Manawa, Wisconsin
Manawa has 18 contaminants exceeding EWG health guidelines out of 32 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Manawa water report →Pewaukee, Wisconsin
Pewaukee has 18 contaminants exceeding EWG health guidelines out of 31 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Pewaukee water report →Wausau, Wisconsin
Wausau has 18 contaminants exceeding EWG health guidelines out of 30 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Wausau water report →Marinette, Wisconsin
Marinette has 18 contaminants exceeding EWG health guidelines out of 30 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Marinette water report →Rhinelander, Wisconsin
Rhinelander has 18 contaminants exceeding EWG health guidelines out of 30 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Rhinelander water report →Waterford, Wisconsin
Waterford has 18 contaminants exceeding EWG health guidelines out of 30 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Waterford water report →Plainfield, Wisconsin
Plainfield has 18 contaminants exceeding EWG health guidelines out of 28 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Plainfield water report →New London, Wisconsin
New London has 18 contaminants exceeding EWG health guidelines out of 27 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full New London water report →Stratford, Wisconsin
Stratford has 18 contaminants exceeding EWG health guidelines out of 27 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Stratford water report →What We Found: Key Patterns
The most frequently detected contaminants exceeding health guidelines across these cities are Bromodichloromethane, Chloroform, Dibromoacetic acid. These appear repeatedly across different water systems and regions.
Water quality varies significantly even within the same state, driven by local geology, agricultural activity, and industrial proximity.
Across all ranked cities, 468 contaminant readings exceed EWG health guidelines, but only 4 exceed EPA legal limits. This gap of 464 highlights how legal standards may not fully protect public health — EPA limits haven't been updated for many contaminants in decades.
Full Rankings Table
| Rank | City | State | Detected | Above Guidelines | Above Legal | People Served |
|---|---|---|---|---|---|---|
| 1 | Marshfield | WI | 39 | 24 | 1 | 18,708 |
| 2 | Weston | WI | 37 | 21 | 0 | 15,045 |
| 3 | Madison | WI | 54 | 20 | 0 | 235,000 |
| 4 | La Crosse | WI | 44 | 20 | 0 | 53,000 |
| 5 | Manitowoc | WI | 35 | 20 | 0 | 34,500 |
| 6 | Bellevue | WI | 35 | 20 | 0 | 0 |
| 7 | Saukville | WI | 32 | 19 | 2 | 4,465 |
| 8 | Hobart | WI | 37 | 18 | 0 | 3,162 |
| 9 | Green Bay | WI | 36 | 18 | 0 | 104,057 |
| 10 | New Franken | WI | 36 | 18 | 0 | 1,875 |
| 11 | Bristol | WI | 35 | 18 | 0 | 1,001 |
| 12 | Waukesha | WI | 34 | 18 | 0 | 70,718 |
| 13 | Onalaska | WI | 34 | 18 | 0 | 18,000 |
| 14 | Oak Creek | WI | 33 | 18 | 0 | 32,104 |
| 15 | Racine | WI | 32 | 18 | 0 | 105,100 |
| 16 | Oshkosh | WI | 32 | 18 | 0 | 63,000 |
| 17 | Manawa | WI | 32 | 18 | 0 | 1,300 |
| 18 | Pewaukee | WI | 31 | 18 | 1 | 8,671 |
| 19 | Wausau | WI | 30 | 18 | 0 | 39,106 |
| 20 | Marinette | WI | 30 | 18 | 0 | 10,968 |
| 21 | Rhinelander | WI | 30 | 18 | 0 | 7,427 |
| 22 | Waterford | WI | 30 | 18 | 0 | 5,368 |
| 23 | Plainfield | WI | 28 | 18 | 0 | 862 |
| 24 | New London | WI | 27 | 18 | 0 | 7,187 |
| 25 | Stratford | WI | 27 | 18 | 0 | 1,651 |
Frequently Asked Questions
What city has the worst tap water in Wisconsin?
Based on 2026 data, Marshfield, WI has the most contaminants exceeding EWG health guidelines among the cities we analyzed.
How are cities ranked in this report?
Cities are ranked by the number of contaminants exceeding EWG health guidelines. These guidelines are typically stricter than EPA legal limits and reflect current scientific research on safe exposure levels.
Is my tap water safe if my city isn't on this list?
Not necessarily. Even cities not on this list may have contaminants of concern. We recommend checking your specific water quality using our free water scan tool.
What's the best water filter for contaminated water?
A reverse osmosis (RO) system is the most effective for removing the widest range of contaminants. For whole-home protection, a combination of RO for drinking water and a whole-home filter for showers and baths is recommended.
Related Reports
Data sources: Environmental Working Group (EWG) Tap Water Database, U.S. EPA Safe Drinking Water Information System (SDWIS)
Last updated: March 2026
Methodology: Contaminant levels are compared against both EPA legal limits (Maximum Contaminant Levels) and EWG health guidelines, which are often stricter and based on the latest scientific research.
