A wider range of organisms is killed by ozonation than by chlorination. It also achieves excellent removal of taste and odors. The reactions, in general, are more rapid than that of chlorination processes. The drawbacks of ozone, like chlorine, is that it may not kill cysts and some other large organisms so these should be eliminated by filtration or other procedures prior to treatment. A major disadvantage is that due to its instability, ozone must be generated before use and the equipment and operating costs can be quite high.
Ozone has an active residual measured in minutes.
This lack of long residual is a significant drawback for its use in large distribution systems.