Wisconsin Tap Water Quality Rankings 2026: 27th in Nation | WaterQ

Wisconsin ranks 27th in our 2026 national tap water quality analysis. The state's standing reflects two distinct challenges: a well-documented PFAS contamination case around Marinette and Peshtigo tied to firefighting foam testing, and a broader, statewide issue with agricultural nitrate affecting groundwater relied on by the roughly one-third of Wisconsin households on private wells.

Key Findings for Wisconsin

Reviewing EPA SDWIS data for 2026, three themes define Wisconsin's water quality landscape:

• Marinette/Peshtigo PFAS: An industrial site in Marinette used for firefighting foam testing has been linked to significant PFAS contamination in nearby groundwater, affecting private wells and prompting bottled water distribution, filtration installations, and ongoing investigation by state regulators.
• Agricultural Nitrate: Central Wisconsin's sandy soils and intensive agriculture, including large-scale irrigation, contribute to elevated nitrate levels in shallow groundwater across a significant portion of the state, affecting both small community systems and private wells.
• Private Well Reliance: Roughly a third of Wisconsin households get their water from private wells, which are not regulated under the Safe Drinking Water Act and are the resident's responsibility to test, particularly for nitrate and bacteria.

Most Common Contaminants in Wisconsin

Here's what Wisconsin residents should know about the contaminants most relevant to their water:

1. PFAS ("Forever Chemicals")

The Marinette/Peshtigo area remains the most significant documented PFAS case in Wisconsin. Affected residents have received bottled water and filtration support while remediation continues, and the case has driven broader statewide PFAS sampling efforts.

2. Nitrate

Nitrate from agricultural fertilizer is one of the most widespread groundwater concerns in Wisconsin, particularly in the central sands region. Community water systems are monitored, but private well owners in agricultural areas should test annually, especially if infants are present.

3. Bacteria (in Karst Regions)

Southwestern Wisconsin's karst (limestone) geology allows surface contaminants to move quickly into groundwater, making private wells in this region more susceptible to bacterial contamination after heavy rain. Annual bacteria testing is particularly important for wells in karst areas.

Wisconsin's Best and Worst Cities for Water Quality

Explore the full breakdown on our Wisconsin water systems page.

Top Performers: Milwaukee and Madison's municipal systems, drawing from Lake Michigan and well-protected groundwater respectively, generally show strong compliance records.

Areas to Watch: The Marinette/Peshtigo area remains under active PFAS investigation, central Wisconsin's agricultural regions warrant nitrate testing for private wells, and karst regions in the southwest require bacteria monitoring.

What Wisconsin Residents Should Do

Given Wisconsin's 27th place ranking, here's what matters most for residents:

1. Check PFAS Status If You're Near Marinette: Residents in the affected area should follow updates from state regulators on testing and filtration support.
2. Search Your System's Record: Use the WaterQ search tool to view your water system's violation history and recent contaminant levels.
3. Test Private Wells Annually: Nitrate and bacteria testing is especially important for the roughly one-third of Wisconsin households on private wells, particularly in agricultural or karst areas.
4. Use Appropriate Filtration: Reverse osmosis or distillation effectively reduces both nitrate and PFAS, while UV treatment can address bacterial concerns in private well systems.

Source: Wisconsin Department of Natural Resources Drinking Water and Groundwater Program, EPA SDWIS 2026 Compliance Data, and WaterQ National Database. For more information on our ranking process, visit our state rankings page.