A filter device includes four couplers attached to four sides, and a casing attached to bottom. A filtering material receptacle may be attached to the casing for filtering the water. A valve member is rotatably received in the housing, and includes six openings and four spaces and to communicate the openings of the valve member with each other, and includes two passageways for communicating with two openings of the valve member. The filtering material may be flushed with the water, and may be forced to change ion or to be cleaned with cleansing agent simply by rotating the valve member relative to the housing.