Fluoride in Wisconsin Drinking Water

Most Wisconsin municipal systems add fluoride to drinking water at approximately 0.7 mg/L, the level recommended by the U.S. Department of Health and Human Services for dental cavity prevention. Natural fluoride in Wisconsin groundwater varies widely — from near zero in many areas to over 4 mg/L in parts of south-central Wisconsin where the geology concentrates it. The EPA MCL of 4 mg/L applies to total fluoride (natural plus added) and exists to prevent skeletal fluorosis, a bone disease caused by long-term high-fluoride exposure. There is also a secondary standard of 2 mg/L to prevent dental fluorosis (cosmetic tooth staining) in children.

The communities most at risk for exceeding the 4 mg/L MCL are typically smaller systems in Dane, Green, and Iowa counties that draw from deep wells with naturally elevated fluoride. These systems sometimes need to reduce or stop intentional fluoridation because the natural level alone approaches or exceeds the limit. For private well users in these areas, a fluoride test is worth doing — if your natural level is above 2 mg/L, point-of-use reverse osmosis on the kitchen tap is the standard fix.