A reservoir is disclosed for a throughfeed for liquid, such as a liquid pump, to be set into operation selectively, from and/or to a body of liquid such as a pond, aquarium or bath. The reservoir includes a container for containing liquid and with an outlet for connecting onto the throughfeed to the body of water. It further includes a refill container which, depending on the level of the liquid in the container, is movable reciprocally between a high position and at least one lower position, and which is connected to an inlet of the reservoir connected to the body of liquid. The refill container includes an overflow along which liquid flows from the refill container into the container in the at least one lower position of the refill container.