A water filter assembly comprising: a filter head including an inlet formed at one side, an outlet formed opposite to the inlet, the inlet and the outlet each communicating with a hollow area formed inside the filter head, and a head key guide formed in an inside face of the hollow area; an inner including a bypass flow path formed at an upper end, a purified water flow path formed adjacent to the bypass flow path, and an inner key guide formed in an inside face of the inner, the inner being inserted to the hollow area of the filter head to move upwardly and downwardly; and a filter body configured to connect a water flow path to the purified water flow path by moving the inner upwardly within the hollow area when the filter body is engaged with the filter head having the inserted inner and configured to connect the water flow path to the bypass flow path by moving the inner downwardly within the hollow area when the filter body is disengaged from the filter head having the inserted inner, the filter body including an inner key for detachably coupling to the inner key guide at an upper part of the filter body and a head key for detachably coupling to the head key guide at a lower part of the filter body, characterized by an elastic member being positioned between the filter head and the inner, to bias the inner downwardly with respect to the filter head, wherein the elastic member is a coil spring; a first spring support located at an upper part of the filter head, the elastic member having a first end inserted in the first spring support; and a second spring support located at an upper face of the inner, the elastic member having a second end inserted in the second spring support; and a vent formed in the filter head to let in and let out air. a filter head including an inlet formed at one side, an outlet formed opposite to the inlet, the inlet and the outlet each communicating with a hollow area formed inside the filter head, and a head key guide formed in an inside face of the hollow area; an inner including a bypass flow path formed at an upper end, a purified water flow path formed adjacent to the bypass flow path, and an inner key guide formed in an inside face of the inner, the inner being inserted to the hollow area of the filter head to move upwardly and downwardly; and a filter body configured to connect a water flow path to the purified water flow path by moving the inner upwardly within the hollow area when the filter body is engaged with the filter head having the inserted inner and configured to connect the water flow path to the bypass flow path by moving the inner downwardly within the hollow area when the filter body is disengaged from the filter head having the inserted inner, the filter body including an inner key for detachably coupling to the inner key guide at an upper part of the filter body and a head key for detachably coupling to the head key guide at a lower part of the filter body, characterized by an elastic member being positioned between the filter head and the inner, to bias the inner downwardly with respect to the filter head, wherein the elastic member is a coil spring; a first spring support located at an upper part of the filter head, the elastic member having a first end inserted in the first spring support; and a second spring support located at an upper face of the inner, the elastic member having a second end inserted in the second spring support; and a vent formed in the filter head to let in and let out air.