Chlorine dioxide for drinking water treatment purposes is generated on-site by theoxidation of chlorite ion or the reduction of chlorate ion. At least 6 technologies for producingchlorine dioxide are commercially available to the drinking water industry. A comparison of the different technologies shows varying levels of impurities in the generator effluent. Based on the generation chemistry, the unused precursor chemicals (chlorite ion, chlorate ion, acid, chlorine, or hydrogen peroxide) potentially can continue to react or form additional unwanted byproducts. Includes 12 references, tables.