A water treatment apparatus, comprising: a filtering portion filtering raw water and including a reverse osmosis filter; a storage portion including a first chamber into which purified water that has been filtered by passing through the reverse osmosis filter flows and a second chamber into which domestic water that has not passed through the reverse osmosis filter flows, a volume of the second chamber is changed depending on a change in a volume of the first chamber; an extraction portion disposed to supply the purified water that has been filtered to a user; a flow path conversion valve configured to convert a flow path to allow purified water to flow into the storage portion or to flow out of the storage portion; and an air supply portion disposed on a flow path connected to the first chamber of the storage portion, in order to supply air to the first chamber of the storage portion, characterized in that the water treatment apparatus comprises a purified water line configured to supply the purified water that has been filtered by passing through the reverse osmosis filter to the storage portion, a purified water supply line configured to supply the purified water supplied by the purified water line to the storage portion, and an extraction line configured to supply the purified water to the extraction portion; wherein the air supply portion is connected to the purified water line and is disposed in a purified water branch portion in which the purified water line is divided into a flow path connected to the extraction line and the purified water supply line; wherein the first chamber is connected to the purified water outlet of the filtering portion and the extraction portion by the purified water supply line; wherein the second chamber is connected to a chamber water line through which the domestic water not filtered in the reverse osmosis filter is supplied and a drain line through which the domestic water is discharged; wherein the flow path conversion valve forms a flow path to allow the domestic water to be supplied to the second chamber, in a case in which the extraction portion is opened, or forms a flow path to allow the domestic water accommodated in the second chamber to be drained through the drain line, in a case in which the extraction portion is closed; and wherein the air supply portion is configured to supply air to the first chamber after the purified water accommodated in the first chamber is completely discharged by opening of the extraction portion, the volume of the first chamber being increased and the volume of the second chamber being reduced by supplying air to the first chamber, and water accommodated in the second chamber being discharged by reducing the volume of the second chamber. a filtering portion filtering raw water and including a reverse osmosis filter; a storage portion including a first chamber into which purified water that has been filtered by passing through the reverse osmosis filter flows and a second chamber into which domestic water that has not passed through the reverse osmosis filter flows, a volume of the second chamber is changed depending on a change in a volume of the first chamber; an extraction portion disposed to supply the purified water that has been filtered to a user; a flow path conversion valve configured to convert a flow path to allow purified water to flow into the storage portion or to flow out of the storage portion; and an air supply portion disposed on a flow path connected to the first chamber of the storage portion, in order to supply air to the first chamber of the storage portion, characterized in that the water treatment apparatus comprises a purified water line configured to supply the purified water that has been filtered by passing through the reverse osmosis filter to the storage portion, a purified water supply line configured to supply the purified water supplied by the purified water line to the storage portion, and an extraction line configured to supply the purified water to the extraction portion; wherein the air supply portion is connected to the purified water line and is disposed in a purified water branch portion in which the purified water line is divided into a flow path connected to the extraction line and the purified water supply line; wherein the first chamber is connected to the purified water outlet of the filtering portion and the extraction portion by the purified water supply line; wherein the second chamber is connected to a chamber water line through which the domestic water not filtered in the reverse osmosis filter is supplied and a drain line through which the domestic water is discharged; wherein the flow path conversion valve forms a flow path to allow the domestic water to be supplied to the second chamber, in a case in which the extraction portion is opened, or forms a flow path to allow the domestic water accommodated in the second chamber to be drained through the drain line, in a case in which the extraction portion is closed; and wherein the air supply portion is configured to supply air to the first chamber after the purified water accommodated in the first chamber is completely discharged by opening of the extraction portion, the volume of the first chamber being increased and the volume of the second chamber being reduced by supplying air to the first chamber, and water accommodated in the second chamber being discharged by reducing the volume of the second chamber.