To reduce power consumption by controlling speed of rotation of a pump while maintaining the water level of the tank of water treatment equipment in a fixed range.

The water treatment equipment includes at least two tanks for storing water to be used in a steel plant and a pump for feeding the water stored in the tank on the upstream side to the tank on the downstream side. A controller groups products supplied to the steel plant, and stores each group and water level change estimated to be generated when the products belonging to the respective groups are supplied in association with each other. When the product is supplied to the steel plant, the group to which the product belongs and the water level change corresponding to the group are read on the basis of the information of the supplied product, and the supply timing of the product to the steel plant is detected or estimated. In accordance with the water level change and the supply timing, the speed of rotation of the pump is controlled so as to maintain the water level of the tank in the fixed range.