Disclosed are a water purifier and a control method thereof, wherein the water purifier can stably supply cold water and cold functional water through one ice thermal storage type cooling system. The water purifier comprises: a feed water flow line through which purified water can be transferred; a gas storage unit; a gas flow line through which gas can be transferred from the gas storage unit; an ice thermal storage tank for performing heat-exchange between the purified water provided by the feed water flow line and iced water and then discharging the cold purified water; and a mixing tank for creating functional water by mixing the cold water cooled in the ice thermal storage tank with the gas flowing through the gas flow line.