A Wisconsin study that shows a connection between viruses in drinking water and human illness is likely to have a national impact and could eventually lead to federal rules requiring treatment of all public water systems, according to experts.

A state law in Wisconsin that required treatment of all municipal drinking water systems in the state was rescinded by the Republican-controlled state Legislature a year ago. State Rep. Erik Severson, R-Star Prairie, sponsored an amendment that removed the requirement, arguing that the rule was an unnecessary financial and bureaucratic burden on communities with already strong water standards.

The EPA-funded study showed that:

• All 14 communities studied during the two-year project had human viruses in their tap water. Of 1,204 samples, 287, or 24 percent, were virus positive.
• The higher the virus concentration, the higher the rate of illness found in each community.
• The type of virus found in drinking water most strongly related to illness was norovirus, the same virus notorious for causing outbreaks on cruise ships.
• During one part of the study, when norovirus was very common in one community’s tap water, the proportion of illness in children younger than 5 years old attributable to their drinking water could have been as high as 63 percent.