Frequent Questions

As of the publication of the Stage 2 Disinfectants and Disinfections Byproducts Rule (Stage 2 DBPR), what are EPA's conclusions for the potential association between chlorinated drinking water and adverse health effects?

EPA concluded that there is at least a potential health concern from chlorinated drinking water based on a collective evaluation of the human epidemiology and animal toxicology data on cancer and reproductive and developmental health effects. EPA also took into consideration the large number of people exposed to chlorinated byproducts in drinking water (more than 260 million). Specifically, EPA concluded that:

  • new cancer data since the Stage 1 Disinfectants and Disinfections Byproducts Rule (Stage 1 DBPR) (63 FR 69389; December 16, 1998) strengthen the evidence of a potential association of chlorinated water with bladder cancer and suggests an association for colon and rectal cancers;
  • current reproductive and developmental health effects data do not support a conclusion at this time as to whether exposure to chlorinated drinking water or disinfection byproducts causes adverse developmental or reproductive health effects, but do support a potential health concern; and
  • there is a need for public health protection beyond that provided by the Stage 1 DBPR, as indicated by the combined health data (71 FR 388, 394; January 4, 2006).

A further discussion of EPA's conclusions on the health effects of chlorinated drinking water, including a summary of the epidemiology studies reviewed for the Stage 2 DBPR, is available in the preamble of the Stage 2 DBPR (71 FR 388, 394-406; January 4, 2006). The rule and additional information are available at

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