Drinking water supplies require disinfection to remove or inactivate microbial pathogens. Disinfectants can react with natural organic matter in the water to form by-products, like trihalomethanes, haloacetic acids, chlorite, and bromate. The Disinfectants and Disinfection Byproducts Rules (Stage 1 DBPR December 16, 1998, and Stage 2 DBPR, January 4, 2006,) aimed to reduce the potential risk of adverse health effects associated with disinfection byproducts (DBPs) throughout water distribution systems. These rules apply to all community water systems and non-transient non-community water systems that either add or deliver a primary or residual disinfectant other than ultraviolet light.
Stage 1 of the DBPR established MCLs for chlorine, chloramine, and chlorine dioxide. It also established MCLGs for total trihalomethanes, haloacetic acids, chlorite, and bromate. Stage 2 of the DPBR built upon Stage 1, by strengthening compliance monitoring requirements. The Stage 2 DBPR required some systems to complete an Initial Distribution System Evaluation (IDSE) to characterize DBP concentrations in their distribution systems and identify locations to monitor DBPs for Stage 2 compliance.
Stage 2 brought three significant changes to the Stage 1 rule:
- water systems choose monitoring locations based on monitoring data;
- compliance determinations switched to locational running annual average calculations at each individual location; and
- required consecutive systems that do not provide their own treatment but receive treated water from a supplying waterworks to comply with the rule.