The invention relates to a device (1) for heating water for a combination shower-WC having a shower arm to which the water can be supplied by means of a pump, said device comprising a tank (2) for holding water, and a heating mechanism which heats the water held in the tank (2), wherein the device (1) is arranged in a structural unit (3) for connection between a water supply and the shower arm of the combination shower-WC, and the heating mechanism comprises a bottom-mounted heating element (4) which at least partially forms a boundary of the tank (2).