A water disconnector unit, in particular for controlling the supply of water to a water circuit of a boiler, comprising, - a hollow casing defining: an inlet chamber and an outlet chamber (26, 28) for connection in flow communication with an external water source and with an external water user, respectively, and an intermediate chamber interposed between the inlet chamber and the outlet chamber, - an inlet valve unit and an outlet valve device which are interposed between the intermediate chamber and the inlet chamber, and between the intermediate chamber and the outlet chamber, respectively, - a discharge valve unit which is interposed between the intermediate chamber and the outside environment and is arranged to put them into flow communication when the difference between the pressure of the inlet chamber and the pressure of the intermediate chamber is below a predetermined threshold value, - first, manually-operable control means associated with the hollow casing and comprising a cam element which is rotatable about a rotation axis (A-A), cooperates simultaneously with the inlet valve unit and with the outlet valve device, and is movable to a closure arrangement or to an opening arrangement in which the cam element arranges both the inlet valve unit and the outlet valve device for closure or for opening, preventing or permitting a flow of fluid from the inlet chamber towards the outlet chamber, respectively, characterized in that said disconnector further comprising second control means which are associated with the hollow casing, can be actuated electrically for opening, and are arranged to bring the inlet valve unit to the opening position irrespective of the arrangement of the cam element. - a hollow casing defining: an inlet chamber and an outlet chamber (26, 28) for connection in flow communication with an external water source and with an external water user, respectively, and an intermediate chamber interposed between the inlet chamber and the outlet chamber, an inlet chamber and an outlet chamber (26, 28) for connection in flow communication with an external water source and with an external water user, respectively, and an intermediate chamber interposed between the inlet chamber and the outlet chamber, - an inlet valve unit and an outlet valve device which are interposed between the intermediate chamber and the inlet chamber, and between the intermediate chamber and the outlet chamber, respectively, - a discharge valve unit which is interposed between the intermediate chamber and the outside environment and is arranged to put them into flow communication when the difference between the pressure of the inlet chamber and the pressure of the intermediate chamber is below a predetermined threshold value, - first, manually-operable control means associated with the hollow casing and comprising a cam element which is rotatable about a rotation axis (A-A), cooperates simultaneously with the inlet valve unit and with the outlet valve device, and is movable to a closure arrangement or to an opening arrangement in which the cam element arranges both the inlet valve unit and the outlet valve device for closure or for opening, preventing or permitting a flow of fluid from the inlet chamber towards the outlet chamber, respectively, characterized in that said disconnector further comprising second control means which are associated with the hollow casing, can be actuated electrically for opening, and are arranged to bring the inlet valve unit to the opening position irrespective of the arrangement of the cam element.