Water switch unit for interrupting and releasing at least one waterway in a sanitary installation, wherein at least one valve seat is formed between at least one water-inflow channel and at least one water-outlet channel (120, 130, 140), the valve seat having inserted on it a bistable magnetic-valve unit, which can be positioned on the valve seat by way of its sealing element; wherein the magnetic-valve unit has a housing tube, which is closed at the end and of which the opening is directed towards the valve seat; wherein the sealing element is connected to a piston element, which is arranged in a displaceable manner in the housing tube; wherein a cam mechanism is formed between the piston element and the housing tube and allows the piston element to move alternately, by means of axial displacement, between an open position and a blocking position; wherein an annular magnet which encloses the housing tube from the outside is provided in order to displace the piston element, it being possible for said annular magnet to be displaced counter to the force of at least one restoring element and to be exchanged for an electric coil which can be fitted over the housing tube, characterized - in that the magnetic-valve unit is inserted into a main body which, on its lower end side, has a surface area in which at least in each case one water-inflow channel and at least one water-outflow channel (120, 130, 160) open out, the at least one valve seat being formed between said channels; - in that an upper side of the main body has formed on it at least one valve mount (124, 134, 142), on which is arranged a cylindrical pipe socket (122, 132, 143), of which the annular upper edge forms the valve seat, - in that a spring element is arranged within the housing tube and prestresses the piston element in the direction of the valve seat, - and in that the main body can be positioned on a flush-mounting connection block which, on an end-side surface area, has at least two openings which correspond with the mouths of the water-inflow and -outflow channels (110, 120, 130, 140) of the main body and continue in in each case at least one water-directing channel (205, 206) leading to a side surface of the flush-mounting connection block. - in that the magnetic-valve unit is inserted into a main body which, on its lower end side, has a surface area in which at least in each case one water-inflow channel and at least one water-outflow channel (120, 130, 160) open out, the at least one valve seat being formed between said channels; - in that an upper side of the main body has formed on it at least one valve mount (124, 134, 142), on which is arranged a cylindrical pipe socket (122, 132, 143), of which the annular upper edge forms the valve seat, - in that a spring element is arranged within the housing tube and prestresses the piston element in the direction of the valve seat, - and in that the main body can be positioned on a flush-mounting connection block which, on an end-side surface area, has at least two openings which correspond with the mouths of the water-inflow and -outflow channels (110, 120, 130, 140) of the main body and continue in in each case at least one water-directing channel (205, 206) leading to a side surface of the flush-mounting connection block.