The expressions of service level about different composition of THMs were built in order to comprehensively describe the effect of residual chlorine and disinfection by-products trihalomethanes(THMs) on water quality in water distribution systems.The expression about water quality service level of residual chlorine and THMs service level was built with three expressions including average values,standard deviation and multiplication.In order to optimize the cost of rechlorination,an expression of chlorinatio...