Chloroform, the most common trihalomethane (THM) in drinking water, has been shown to be a carcinogen in rodents and thus poses a risk to consumers of drinking water. Reduction of THMs can be accomplished by using a disinfectant that does not generate THMs, by reducing precursor concentrations prior to chlorination, or by reducing THMs after formation. Modification of existing treatment facilities for THM reduction must be carefully controlled so that the microbiological quality of the drinking water is not compromised.