Chlorine dioxide
Chlorine dioxide has been approved by the U.S. Environmental Protection Agency as a primary disinfectant of potable water since 1945. Chlorine dioxide does not produce any carcinogenic byproducts like chlorine when used in the purification of drinking water that contains natural organic compounds such as humic and fulvic acids; chlorine tends to form halogenated disinfection byproducts such as trihalomethanes. Drinking water containing such disinfection byproducts has been shown to increase the risk of cancer. ClO2 works differently from chlorine; its action is one of pure oxidation rather than halogenation, so these halogenated byproducts are not formed.