A water-quality control device 5 that controls the water quality of water flowing in a water pipeline and that is provided with: a first determination unit 51 that, on the basis of measurement results from a turbidimeter that measures the turbidity of the water, from a colorimeter that measures the color of the water, and from a residual chlorine concentration meter that measures the residual chlorine concentration of the water, determines whether the water pipeline needs to be drained; and a second determination unit 52 that, when the water pipeline is drained, controls the amount of drainage such that the turbidity of the water does not exceed a threshold value.
