A water pump includes an impeller provided at a first end of a rotational shaft supported by a body via a bearing, a mechanical seal provided between the impeller and the bearing, a draining hole introducing a water drop leaked from an impeller side via the mechanical seal to a reservoir provided at a bottom of the body and having a side opening, a plugging member provided at the side opening of the reservoir for liquid-tightly sealing the reservoir, and an opening portion provided at the plugging member for communicating the reservoir and an atmosphere side.