Ozone is a powerful and naturally unstable oxidizing gas. In solution, it retains its strong oxidizing characteristics and resembles chlorine in many reactions. Ozone maintains an "ozone demand" which must be satisfied before its microbiological traits are exhibited.

Like chlorine, ozone is affected by pH, temperature, organics, solvents and accumulated reaction products; these detract from its desired effect. Unlike chlorine, however, it does not contribute to the chloride content of the water system. Ozone is nonpolluting and harmless to aquatic organisms because it decomposes photochemically to form oxygen. The cost of ozone is a major detriment to its use.

Common treatment residuals are 0.1 ppm in the industrial water system fed on either a continuous or intermittent basis. Like other oxidizing microbiocides, ozone has been known to contribute to lumber deterioration by delignification when overfed. Therefore, residual control is important. Recently ozone has been touted as a stand alone industrial water treatment, providing corrosion and deposit inhibition as well as microbiological control. To date there is no accepted scientific proof that substantiates these claims.