A water pump includes a rotation member, a hollow shaft portion having an opening on one end and connected to the rotation member for unitary rotating with the rotation member, an impeller connected to the shaft portion for unitary rotating with the shaft portion, a body defining a fluid chamber in which the impeller is rotated, a bearing for rotatably supporting the shaft portion on the body, a sealing member provided between the shaft portion and the body for sealing the fluid chamber and a cover portion for substantively closing the opening of the shaft portion.