that the valve element 62 is opened the valve element then remains open until the prestressing force of the spring 72 is greater than the water pressure in the water supply line 38 and the prestressing force of the spring 66 the control valve 36 is connected to the line separator 34 via at least one connecting channel 78 in the wall part 56 the line separator 34 has a control piston 80 which can be displaced in the second cylinder part 54 and in its central region contains a coaxial injector through passage 82 of which the nozzle 84 is directed towards a chamber 86 which is connected to the water heater 22 via a connecting line 85 in the absence of water pressure a spring 88 prestresses the control piston 80 into the rest position against the valve seat 87 and thus closes the connecting channel 78 between the control valve 36 and the injector through passage 82 in this rest position the control piston 80 opens a through passage 89 from the chamber 86 of the control piston 80 to an annular channel 90 and a line 92 which opens out into the toilet bowl as a result of which the line channelling between the water supply line 38 and the water heater 72 is separated in the case of any implosion in the water supply line 38 it is not possible on account of the non return valve 94 described hereinbelow for any water to be taken back into the water supply line 38 from the water heater and the downstream douche head.