Abstract: The invention relates to a valve (6) for a tap. Said valve (6) comprises a main water channel (17, 19), through which the water flows to a tap or similar. The main water channel (17, 19) can be sealed by an elastic membrane (20), the latter (20) always opening when the pressure on its upper side is lower than that on its underside. The pressure on the upper side is generated by a derived circuit (27, 28; 30, 31), which can conduct water from the main water channel (17) onto the upper side of the membrane (20). The membrane (20) is controlled by a pedal. The fact that the derived circuit consists of two zones (27, 28 and 30, 31), one (27, 28) of which is open and the other (30, 31) closed, enables operation at both low and high water pressures. Two permanent magnets (22, 23) are used to transmit the force for opening and closing the two zones of the derived circuit (27, 28; 30, 31), providing a perfect seal for the valve in relation to the environment.