Over 98 percent of U.S. water supply systems that disinfect drinking water use chlorine. In the US we have depended on chlorine as our drinking water disinfectant for nearly a century. Public health officials heralded water chlorination as one of the greatest public health achievements of this century. Chlorine-based disinfectants are the only disinfectants that provide lasting residual protection to protect the water from waterborne disease throughout the distribution system from treatment plant to the consumer's tap. Alternatives to chlorination for primary disinfection such as ozone or ultraviolet light can not provide this residual protection.
All chemical disinfectants produce byproducts.
Chlorination byproducts have been well studied compared to the byproducts of alternatives which are just beginning to be studied. This rule was developed by the EPA with the broad support of environmentalists, water utilities, and chlorine producers. It will be finalized in November 1998. The new rule will require water utilities to use a process called enhanced coagulation to remove organic material from the water. Organic matter, in combination with any disinfectants, produces disinfection byproducts.