A water treatment apparatus comprising: a filter unit (110, 210) purifying raw water; a storage tank (170, 270) connected to the filter unit (110, 210) and storing purified water which has been filtered through the filter unit (110, 210); an electrolytic sterilizer (130, 230) installed between the filter unit (110, 210) and the storage tank (170, 270), electrolyzing only purified water which has been filtered through a portion of the filter unit (110, 210) to generate sterilization water, and supplying the sterilization water to the storage tank (170, 270); a drain unit (150, 250) connected to the storage tank (170, 270) and discharging water accommodated in the storage tank (170, 270); and a control unit (190, 290) controlling a water purification mode of the filter unit (110, 210) and a sterilization mode through the electrolytic sterilizer (130, 230) and the drain unit (150, 250), wherein the filter unit (110, 210) comprises a sediment filter (111, 211), a pre-carbon filter (112, 211), and a reverse osmosis, RO, membrane filter (113, 213) or a hollow fiber membrane filter, sequentially connected through a water purification line, and the electrolytic sterilizer (130, 230) is installed in a sterilization water line (142, 242) diverged from a flow path between the sediment filter (111, 211) and the RO membrane filter (113, 213) or the hollow fiber membrane filter and connected to the storage tank (170, 270), wherein only purified water which has passed through the sediment filter (111, 211), or the sediment filter (111, 211) and the pre-carbon filter (112, 211) provided at a front stage of the RO membrane filter (113, 213) or the hollow fiber membrane filter is led via the sterilization water line (142, 242) to the electrolytic sterilizer (130, 230) and is electrolyzed to generate sterilization water, and wherein the sterilization water generated by the electrolytic sterilizer (130, 230) is supplied to the storage tank (170, 270) through the sterilization water line (142, 242). a filter unit (110, 210) purifying raw water; a storage tank (170, 270) connected to the filter unit (110, 210) and storing purified water which has been filtered through the filter unit (110, 210); an electrolytic sterilizer (130, 230) installed between the filter unit (110, 210) and the storage tank (170, 270), electrolyzing only purified water which has been filtered through a portion of the filter unit (110, 210) to generate sterilization water, and supplying the sterilization water to the storage tank (170, 270); a drain unit (150, 250) connected to the storage tank (170, 270) and discharging water accommodated in the storage tank (170, 270); and a control unit (190, 290) controlling a water purification mode of the filter unit (110, 210) and a sterilization mode through the electrolytic sterilizer (130, 230) and the drain unit (150, 250), wherein the filter unit (110, 210) comprises a sediment filter (111, 211), a pre-carbon filter (112, 211), and a reverse osmosis, RO, membrane filter (113, 213) or a hollow fiber membrane filter, sequentially connected through a water purification line, and the electrolytic sterilizer (130, 230) is installed in a sterilization water line (142, 242) diverged from a flow path between the sediment filter (111, 211) and the RO membrane filter (113, 213) or the hollow fiber membrane filter and connected to the storage tank (170, 270), wherein only purified water which has passed through the sediment filter (111, 211), or the sediment filter (111, 211) and the pre-carbon filter (112, 211) provided at a front stage of the RO membrane filter (113, 213) or the hollow fiber membrane filter is led via the sterilization water line (142, 242) to the electrolytic sterilizer (130, 230) and is electrolyzed to generate sterilization water, and