Drinking water contaminated by bacteria, viruses and protozoa can cause sudden or ongoing intestinal illness. Although all public water utilities in Dane County, except for the Town of Dane, chlorinate drinking water to kill microbes, occasional problems can occur. One potential problem area is that private well water is not chlorinated at all.
Examples of serious problems are:
- In 1993 in Milwaukee, 400,000 people became ill when a water purification plant failure allowed the protozoa Cryptosporidium, to enter the system.
- In urban Dane County, in 2006, the newly installed drinking water system of a new office building was heavily contaminated with bacteria because the system was not sufficiently protected and disinfected during construction.