Chlorine dioxide has been used in potable water treatment for controlling taste and odor and for removing iron and manganese. For control of bacteria and viruses, chlorine dioxide is as effective as free chlorine and is superior to free chlorine for controlling cysts. Chlorine dioxide is an effective drinking water disinfectant when combined with a residual disinfectant such as chlorine or chloramines. Even with its positive features, chlorine dioxide has not been widely accepted. There is a concern that the total or individual oxidants of chlorine dioxide will be regulated to such a low concentration that extensive treatment will be required to achieve these levels. Residual concentrations of 0.5 mg/L and 1.0 mg/L have been recommended. Field studies have been initiated by the U.S. Environmental Protection Agency at Jefferson Parish, Louisiana and Evansville, Indiana to evaluate the biocidal effectiveness of chlorine dioxide and control the total oxidants to acceptable levels.