Regulation Spotlight:

Stage 2 Disinfectant Byproducts Rule


The Environmental Protection Agency (EPA) proposed the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR) to reduce disease incidence associated with dangerous chemical byproducts that form when public water supply systems add disinfectants. The Stage 2 DBPR will supplement existing regulations by requiring water systems to meet disinfection byproduct maximum contaminant levels (MCLs) at each monitoring site in the distribution system. The proposal also contains a risk-targeting approach to better identify monitoring sites where customers are exposed to high levels of disinfection byproducts (DBPs). This proposed regulation will reduce DBP exposure and provide more equitable health protection, and will result in lower cancer and reproductive and developmental risks.


Chlorine and other chemical disinfectants have been widely used by public water systems as a principal barrier to microbial contaminants in drinking water. DBPs are formed when certain disinfectants interact with organic and inorganic materials in source waters. The levels of DBPs in drinking water can vary significantly from one point in a distribution system to another. Epidemiology and toxicology studies have shown a link between bladder, rectal and colon cancers and DBP exposure. In consideration of the large number of people exposed to DBPs (approximately 254 million Americans), the EPA has proposed additional DBP control measures beyond those already required for public water systems.


The Stage 2 DBPR will protect public health by supplementing existing drinking water regulations with risk-targeted monitoring and compliance determinations for current disinfection byproduct MCLs. This regulation will apply to all systems that add a disinfectant other than ultraviolet light. Under the Stage 2 DBPR, systems will conduct an Initial Distribution System Evaluation (IDSE) to identify locations with high disinfection byproduct concentrations. These locations will then be used as the sampling sites for DBP compliance monitoring.

Under the Stage 2 DBPR, compliance with the maximum contaminant levels for two groups of disinfection byproducts, total trihalomethanes (TTHM) and haloacetic acids (HAA5) will be calculated for each monitoring location in the distribution system. This approach, referred to as the locational running annual average (LRAA), differs from current requirements, which determine compliance by calculating the running annual average of samples from all monitoring locations across the system. The Stage 2 DBPR would also require systems to determine if they are experiencing short term peaks in DBP levels referred to as “significant excursions.” Systems experiencing significant excursions would be required to review their operational practices and work with their state to determine actions that may be taken to prevent future excursions.

The new requirements provide more consistent protection from DBPs across the entire distribution system and the reduction of DBP peaks, requiring only those systems with the greatest risk to make capital improvements.

Cost of the Regulation

The Stage 2 DBPR will result in increased costs to public water systems and states. The annual cost of the rule is expected to be $54.3 to $63.9 million. Public water systems will bear approximately 98 percent (equivalent to $53.1 to $62.8 million) of this total cost, with states incurring the remaining 2 percent ($1.1 to $1.2 million).

Current Status

The proposed Stage 2 Disinfectants and Disinfection Byproducts Rule was published in the August 18, 2003 Federal Register. The comment period was extended by 60 days, and comments were accepted until Friday, January 16, 2004. Subsequent to review of comments, a final rule will be published. However, it may be 12-18 months before the final rule takes effect.

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