PROBLEM TO BE SOLVED: To provide an operation control system of disinfectants in water purification treatment facilities, capable of controlling residual chlorine in a region with a large daily variation (seasonal variation) in water demand, while no conventional method for controlling clean water quality takes the relations between the water supply process and a plurality of disinfectants into account at the same time.SOLUTION: A control system 10 for injecting disinfectants in water service includes: means for determining the water quantity to be treated based on the estimation of water demand; a water quality meter installed at a site for injecting a disinfectant, which measures the water quality for calculating the concentration of the disinfectant and the concentration distribution of the disinfectant; a pipe network information data base which stores the pipe network information for calculating the concentration of the disinfectant and the concentration distribution of the disinfectant; means 300 which
