A connecting device is arranged for connecting a beverage machine (2) with an external liquid delivery system (3) to supply such liquid to the machine (2). The connecting device (1) has: a device body (16); an inlet (10) for a fluid connection to the external system (3); an outlet (13) for delivering liquid from the external system (3) via the inlet (10) to the machine (2); a valve arrangement (12a, 12b) switchable between an open configuration for establishing a fluidic connection between the inlet (10) and the outlet (13) and a closed configuration for interrupting the fluidic connection; and a control unit (14) for switching the valve arrangement (12a, 12b) between its open configuration and its closed configuration. The device body (16) has an assembly arrangement (16c; 16b, 16d, 16e, 16f) for reversibly or irreversibly assembling the device body (16) to the machine (2).