The disinfection of public water supplies has been used to prevent the transmission of waterborne diseases throughout the worlds. Although chlorine has been used as the primary disinfactant, its safety was first questioned in 1974 when chlorination of drinking water was found to result in the formation of trihalomethanes(THMs). Chlorine dioxide was selected as one alternative disinfactant. But the application of chlorine dioxide in water treatment has been limited because of concerns about the health effects of DBPs. In these experiments, chlorine dioxide showed the effective inactivation on both total coliforms and HPC at 3.0 mg $ClO_2/L$. The bactericidal effects of chlorine dioxide showed a tendency to increase as pH decreased, but the differences were not so sizable.