This is an example of what can be found in well water: There are a number of naturally-occurring contaminants in Wisconsin groundwater. The more common ones are: arsenic, radon, bacteria, parasites, viruses, iron, manganese, hydrogen sulfide, sulfate, chloride, barium, lead, zinc, copper, radium, uranium, and fluoride.

Some of these (radium, radon, bacteria, parasites, viruses, arsenic, uranium, and lead) pose a health risk if present a high levels. This list is not an all inclusive listing of possible contaminants.

State health officials have also identified a number of human-made contaminants that are showing up in the groundwater supplies. They are: nitrate nitrogen, atrazine, arsenic, benzene, toluene, alachlor, Trichloroethylene (TCE), bacteria, parasites and viruses, and chloroform All of these compounds are a health concern when present in concentrations above established health advisory levels