Disinfection By-products

Public drinking water supplies must be disinfected to control microorganisms and infectious disease, but the disinfectants used (commonly chlorine based) may react with natural organic and inorganic matter in source water and distribution systems to form disinfection by-products (DBPs). Results from toxicology studies have shown several DBPs (e.g., bromodichloromethane, bromoform, chloroform, dichloroacetic acid, and bromate) to be carcinogenic in laboratory animals. Other DBPs (e.g., chlorite, bromodichloromethane, and certain haloacetic acids) have also been shown to cause adverse reproductive or developmental effects in laboratory animals. Several epidemiology studies have suggested some association between certain cancers (e.g., bladder) or reproductive and developmental effects and exposure to chlorinated surface water or DBPs. Environmental Health Investigations Branch staff have conducted studies on the reproductive effects of DBPs called trihalomethanes; mapped DBP levels; and assisted in policy considerations.

Because a large percentage of the population drinks water from public systems and is thus potentially exposed to DBPs, health risks associated with DBPs, however small, need to be taken seriously. If pregnant women or others are concerned about possible risks, they can check the levels on reports from their water companies, which must maintain certain allowable DBP levels set by the Environmental Protection Agency. However, not all DBPs are measured or regulated. If the DBP levels in your drinking water are on the high side of allowable levels, bottled water may be consumed. Bottled water is not regulated in the same way as public drinking water supplies.