The invention relates to a water system comprising a circuit with a water drive pump that rotates due to the action of a motor, a discharge valve, and a washing spray gun including an activation trigger. When the trigger is actuated, pressurised water flows from the outlet nozzle of the gun and, when the trigger is released, the flow of water from the nozzle is interrupted, thereby stopping the rotation of both the motor and the drive pump. The device comprises a first pressure switch (1) and a second pressure switch (2) together with a non-return valve (6) and a discharge valve (3) having a hydraulic pilot acting against the resistance of a spring (3b).
