Ozone has been used for the treatment of drinking water since 1906 when it was installed in the city of Nice, France, for disinfection purposes. Although many water treatment plants throughout the world still use ozone primarily for disinfection most modern plants rely on ozone to perform one or more oxidation functions. Applications for ozonation now include oxidation of inorganic and organic materials, flocculation and microflocculation for removal of turbidity or suspended solids, and promotion of aerobic biological processes conducted in filter and adsorption media. Bacterial disinfection, viral inactivation, oxidation of soluble iron and manganese, color removal, taste and odor removal, algae control, cyanides, sulfides, nitrites, trihalomethanes, costs, and health effects are discussed. Includes 58 references, tables, figures.