A dishwashing machine comprises a wash tub (3), an electric pump (87) for supplying water from a bottom (3a, 88) of the tub (3) to a sprinkler system (83-86), a switchable device (40), operatively set downstream of a delivery section of the electric pump (87), for controlling supply of water to the sprinkler system (83-86), a water-storage system (30, 45, 46, 50) comprising a tank (30) and a control system including control means for issuing a command for start-up of at least one program for treatment of the dishes that includes at least one step of charging water from the water mains to the tub (3), at least one step of treatment of the dishes, and at least one the step of filling of the tank (30). The switchable device (40) comprises a casing (41), mounted displaceable within which is a distributor member, which can be actuated by an actuator for assuming a plurality of operating positions, amongst which at least one position of opening a first outlet (44), for supplying a first sprinkler (83), and of simultaneously closing another outlet (43), for supplying a second sprinkler (84). The casing (41) of the switchable device (40) has a third outlet (45) that is always open; i.e., it is open irrespective of the operating position assumed by the distributor member. The third outlet (45) is connected via a third pipe (46) to a first opening (39a) of the tank (30) that functions alternatively as inlet and as outlet for the water with respect to the cavity of the tank. Between the third outlet (45) and the first opening (39a) of the tank (30) valve means (50) operate, which can be controlled independently of the switchable device (40).