EPA sets enforceable rules for disinfectants and disinfectant byproducts (DBPs) in drinking water. DBP formation is influenced by precursor concentration and the type of disinfection used. For example, chlorination of water that is high in organic matter (TOC) may form trihalomethanes (THM) or haloacetic acids (HAA5), particularly in warmer temperatures. Other disinfectants, such as UV light or ozone, may create bromate (BrO3-) or chlorite (ClO2-). THM formation may be decreased by first adding ammonia prior to chlorine to form chloramines.
Depending on the treatment, chlorine, chloramines, bromate, chlorine dioxide and chlorite, TOC, THM, and HAA monitoring must be done. EPA has established residual goals for chlorine, chloramines, and chlorine dioxide and Maximum Contaminant Levels (MCLs) for total THMs, HAA, BrO3- for plants that use ozone, and ClO2- for plants that use chlorine dioxide. Some states, such as CA, have also established limits for nitrosamines.
TOC is not regulated; however, TOC must be removed below certain concentrations dependent upon source water alkalinity. Removal of TOC helps to minimize THM formation.