To always stably supply drinking water of high safety to users by deciding whether or not maintenance is necessary for a water cleaning plant simply by a specialist and controlling the plant properly.

At least one water cleaning plant 12 installed in waterworks, an observation device 13 for observing the water treatment conditions of the water cleaning plant 12, a data accumulating device 17 for collecting data observed by the observation device 13, and a display device 18 for displaying the data collected in the data accumulating device 17 are provided. The observation device 13 has a flow rate measuring device 14 for measuring the flow rate of water to be treated by the water cleaning plant 12 and pressure difference measuring device 15 for measuring the pressure difference between water on the upstream side of the water cleaning plant 12 and water on the downstream side of the plant 12. A detector for reading data collected by the data accumulating device 17 can be provided together with the display device 18.