The present invention provides a method for controlling a drinking-water supply device, the method comprising: a first step of connecting a guide pipe of a case separable from a cabinet to form a channel through which water moves from the case to the cabinet; a second step of supplying the cabinet with sterile water electrolyzed by an electrolytic module included in the case; and a third step of supplying the cabinet with water which has not passed through the electrolytic module included in the case, wherein the sterilization water and the water are supplied to the cabinet from the case via the guide pipe in the second step and the third step.