A method for producing a field effect transistor, in which a plurality of layers are in each case deposited, planarized and etched back, in particular a gate electrode layer, is disclosed. Thus, the user can operate the push button by his one hand only, so as to switch and adjust the water flow, thereby facilitating the user switching and adjusting the water flow of the shower head. An undesired escape of the mass from the container lid can thus be prevented. The condition of equal voltages on the differential lines is detected by an equal-voltage detector that generates a power-down signal when the differential lines are at equal voltages for a period of time.