a device for the preparation of hot water includes a water reservoir , a tube system coupled to the water reservoir and a heating unit to heat the water passing through the tube system from the water reservoir . a float switch detects a water level in the water reservoir . the float switch includes a float arranged in the tube system to measure the water level in the water reservoir and a sensor responsive to the float to transmits a signal to an electronic component to activate the heating unit in dependence on the water level in the water reservoir .