A water treatment apparatus comprising: a filter unit including a reverse osmosis filter to supply purified water filtered from raw water by the reverse osmosis filer to a purified water line and to supply unpurified water unable to be filtered from the raw water by the reverse osmosis filer to an unpurified water line; a storage unit in fluid communication with the filter unit and including a storage member in which purified water is stored and from which purified water is discharged and a housing, which includes the storage member disposed therein, and, through which unpurified water flows in and out; and a flow path changing valve between and in fluid communication with the filter unit and the storage unit, the flow path changing valve allowing: - unpurified water to flow from the housing when purified water is stored in the storage member, and - purified water to be discharged from the storage member when unpurified water flows into the housing; wherein the flow path changing valve comprises: a first body portion with three ports (411, 412, 413) configured for putting in fluid communication the reverse osmosis filter and the housing; and a second body portion with a. connection path having a first end and a second end, said second body portion being connected to the first body portion, and configured for putting in fluid communication the storage member and the reverse osmosis filter, wherein said unpurified water line for unpurified water from the reverse osmosis filter puts in fluid communication the reverse osmosis filter with a residential water port of the first body portion, a drain line branching off from the unpurified water line for draining externally, wherein a drain branch line puts in fluid communication a drain port of the first body portion with the drain line for draining externally, wherein an inlet-outlet line puts in fluid communication the housing and an inlet-outlet port 413 of the first body portion, wherein said purified water line for purified water from the reverse osmosis filter puts in fluid communication the reverse osmosis filter with the storage member, a discharge line branching off from the purified water line, said discharge line being connected to a first end of the connection path in the second body portion, wherein the flow path changing valve allows the inlet-outlet line to be in fluid communication with the drain branch line via a first port and a second port of the first body portion when purified water is stored in the storage member, and allows the inlet-outlet line to be in fluid communication with the unpurified water line via the first port and a third port of the first body portion when the purified water stored in the storage member is discharged to a water discharge member connected either directly to the discharge line or indirectly to the discharge line via the second end of the connection flow path in the second body portion. a filter unit including a reverse osmosis filter to supply purified water filtered from raw water by the reverse osmosis filer to a purified water line and to supply unpurified water unable to be filtered from the raw water by the reverse osmosis filer to an unpurified water line; a storage unit in fluid communication with the filter unit and including a storage member in which purified water is stored and from which purified water is discharged and a housing, which includes the storage member disposed therein, and, through which unpurified water flows in and out; and a flow path changing valve between and in fluid communication with the filter unit and the storage unit, the flow path changing valve allowing: - unpurified water to flow from the housing when purified water is stored in the storage member, and - purified water to be discharged from the storage member when unpurified water flows into the housing; - unpurified water to flow from the housing when purified water is stored in the storage member, and - purified water to be discharged from the storage member when unpurified water flows into the housing; a first body portion with three ports (411, 412, 413) configured for putting in fluid communication the reverse osmosis filter and the housing; and a second body portion with a. connection path having a first end and a second end, said second body portion being connected to the first body portion, and configured for putting in fluid communication the storage member and the reverse osmosis filter,