Drinking Water Contaminant Guides

Radium is the most common federal drinking water violation in Wisconsin — and most people who have it in their water have no idea.

Gross alpha is the catch-all measurement for radioactive particles in your water — including radium, uranium, and polonium — and Wisconsin has the second-highest count of gross alpha violations of any contaminant in the state.

Nitrate contamination from fertilizer and manure is the most widespread agricultural water quality issue in Wisconsin — and it has a hard EPA limit because high nitrate is acutely dangerous to infants.

Arsenic in Wisconsin drinking water comes from naturally arsenic-rich bedrock — primarily in the Fox River valley and the Sturgeon Bay region — and the EPA limit was tightened in 2006 because long-term exposure causes cancer.

PFAS — 'forever chemicals' — have shown up in dozens of Wisconsin water systems, and the EPA finalized the first-ever federal limits for them in 2024.

TTHMs are a byproduct of chlorine disinfection — the same process that keeps your water safe from bacteria also creates these chemicals, and Wisconsin's northern and rural systems are hit hardest.

HAA5 is the other major disinfection byproduct — formed the same way as TTHMs when chlorine meets organic matter in your water supply.

Fluoride in Wisconsin water comes from two sources — natural geology and intentional addition for dental health — and the distinction matters because the EPA limit only applies to total fluoride regardless of source.

Uranium in Wisconsin groundwater is a natural radionuclide — it comes from the same geology that produces radium and gross alpha, concentrated in the central part of the state.

Lead in Wisconsin drinking water doesn't come from the source — it comes from the pipes, and the EPA's tighter Lead and Copper Rule Improvements take effect in 2027.