A pump, comprising: a main body having an inlet defined through the main body; an outlet defined through the main body and spaced apart from the inlet; an assembling part formed in one of two side surfaces of the main body, and having an assembling chamber defined in a center of the assembling part; a mounting part formed in the assembling chamber and having a discharging chamber defined in a center of the mounting part; a mounting cover mounted on the mounting part of the main body and closing the discharging chamber; a motor mounted on the other side surface of the main body and having a shaft mounted through the main body and extending in the discharging chamber; an impeller mounted on the shaft and located in the discharging chamber; and a covering assembly mounted on the assembling part and closing the assembling chamber the pump being characterized in that the mounting part further has an influent hole defined through an inner surface of the discharging chamber and communicating with the inlet; an effluent hole defined through the inner surface of the discharging chamber, spaced apart from the influent hole, and communicating with the outlet; and a storage hole defined through an upper part of the assembling chamber and communicating with the effluent hole; in that the covering assembly has a storage chamber formed between an inner surface of the covering assembly and the assembling chamber, and communicating with the storage hole and the discharging chamber; and in that the mounting cover has a first returning hole defined through the mounting cover, and communicating with the discharging chamber and the storage chamber. a main body having an inlet defined through the main body; an outlet defined through the main body and spaced apart from the inlet; an assembling part formed in one of two side surfaces of the main body, and having an assembling chamber defined in a center of the assembling part; a mounting part formed in the assembling chamber and having a discharging chamber defined in a center of the mounting part; an inlet defined through the main body; an outlet defined through the main body and spaced apart from the inlet; an assembling part formed in one of two side surfaces of the main body, and having an assembling chamber defined in a center of the assembling part; a mounting part formed in the assembling chamber and having a discharging chamber defined in a center of the mounting part; a mounting cover mounted on the mounting part of the main body and closing the discharging chamber; a motor mounted on the other side surface of the main body and having a shaft mounted through the main body and extending in the discharging chamber; an impeller mounted on the shaft and located in the discharging chamber; and a covering assembly mounted on the assembling part and closing the assembling chamber the pump being characterized in that the mounting part further has an influent hole defined through an inner surface of the discharging chamber and communicating with the inlet; an effluent hole defined through the inner surface of the discharging chamber, spaced apart from the influent hole, and communicating with the outlet; and a storage hole defined through an upper part of the assembling chamber and communicating with the effluent hole; in that the covering assembly has a storage chamber formed between an inner surface of the covering assembly and the assembling chamber, and communicating with the storage hole and the discharging chamber; and in that the mounting cover has a first returning hole defined through the mounting cover, and communicating with the discharging chamber and the storage chamber. a storage chamber formed between an inner surface of the covering assembly and the assembling chamber, and communicating with the storage hole and the discharging chamber; and in that the mounting cover has a first returning hole defined through the mounting cover, and communicating with the discharging chamber and the storage chamber.