A water treatment device comprising: a filtering unit for filtering raw water, a storage unit comprising a first chamber for storing purified water, having passed through at least a portion of filters provided in the filtering unit and thus filtered, a second chamber in which raw water is supplied, a housing having an internal space formed therein for storing the purified water filtered by the filtering unit; and a partition member dividing the internal space of the housing into the first chamber and the second chamber, the partition member being deformed according to volume changes of the first chamber and the second chamber, an extraction unit installed to provide a user with the purified water, having been filtered, by using pressure of raw water, a sterilizing water supply unit for supplying sterilizing water to at least one of the storage unit and the extraction unit, and a control unit for controlling driving of the sterilizing water supplying unit, and opening and closing of a channel connecting a downstream of sterilizing water supply unit and an upstream of the storage unit or the extraction unit to supply the sterilizing water to at least one of the storage unit and the extraction unit, characterized in that the sterilizing water supply unit is installed in a sterilizing water line branched from a filtering unit line provided in the filtering unit, such that water passed through at least a portion of the filters provided in the filtering unit may flow through the sterilizing water line, wherein the filtering unit line is connected to the first chamber through a purified water supply line such that purified water filtered in the filtering unit may flow into the first chamber, wherein the sterilizing water line is connected to the purified water supply line such that the sterilizing water generated by the sterilizing water supply unit may flow into the first chamber, and wherein the purified water supply line is connected to the extraction unit such that when raw water is supplied to the second chamber, the purified water or the sterilizing water stored in the first chamber is discharged to the extraction unit by the pressure of raw water. a filtering unit for filtering raw water, a storage unit comprising a first chamber for storing purified water, having passed through at least a portion of filters provided in the filtering unit and thus filtered, a second chamber in which raw water is supplied, a housing having an internal space formed therein for storing the purified water filtered by the filtering unit; and a partition member dividing the internal space of the housing into the first chamber and the second chamber, the partition member being deformed according to volume changes of the first chamber and the second chamber, an extraction unit installed to provide a user with the purified water, having been filtered, by using pressure of raw water, a sterilizing water supply unit for supplying sterilizing water to at least one of the storage unit and the extraction unit, and a control unit for controlling driving of the sterilizing water supplying unit, and opening and closing of a channel connecting a downstream of sterilizing water supply unit and an upstream of the storage unit or the extraction unit to supply the sterilizing water to at least one of the storage unit and the extraction unit, characterized in that the sterilizing water supply unit is installed in a sterilizing water line branched from a filtering unit line provided in the filtering unit, such that water passed through at least a portion of the filters provided in the filtering unit may flow through the sterilizing water line, wherein the filtering unit line is connected to the first chamber through a purified water supply line such that purified water filtered in the filtering unit may flow into the first chamber, wherein the sterilizing water line is connected to the purified water supply line such that the sterilizing water generated by the sterilizing water supply unit may flow into the first chamber, and wherein the purified water supply line is connected to the extraction unit such that when raw water is supplied to the second chamber, the purified water or the sterilizing water stored in the first chamber is discharged to the extraction unit by the pressure of raw water.