Chlorine in Drinking Water Treatment

FAQs - Water Quality and Public Health

Chlorine is used as a disinfectant by most public water systems to kill harmful microorganisms during the water treatment process. The use of chlorine, in carefully controlled dosages, provides a significant public health improvement. The Milwaukee Water Works uses a liquid form of chlorine.

As the water leaves the treatment plant, ammonia is added to change the free chlorine to chloramine. This is a very stable form of chlorine disinfectant that maintains the residual protection in the distribution system. The Wisconsin Department of Natural Resources (DNR) requires water utilities to maintain a detectable level of disinfectant throughout the distribution system to maintain bacteriological protection.

The Disinfectants/Disinfection Byproduct Rule sets a maximum chlorine level of 4.0 mg/L (4.0 ppm) for finished water. The DNR requires the water leaving a treatment plant to have a minimum chlorine level of 1.0 mg/L (1.0 ppm). The water leaving Milwaukee's two treatment plants has a chlorine residual in the range of 1.30 - 1.84 mg/L.