The water tank (1) for the pump has at the bottom one or several pump chambers which can be separated from the tank by a shut-off flap. The pump chamber is cylindrical and closed off by a plunger which moves up and down in the chamber. The pump chamber has on its a base an outflow which can be closed off by a shut-off valve. The pump chamber is connected via a water outlet to an ascending pipe on whose outlet a reverse flow check valve is fitted.
