A device in connection with a hand-operated working machine with a water flow directed to the working tool comprises a first control which is a control (15) for a drive motor (3) for the tool, and a second control which is a control (17) for the water supply to the tool. A water control valve (45) in a water supply conduit (14) can be adjusted to adopt chosen opening positions, and is arranged constantly to be kept open in any chosen opening position when the motor is running the tool under influence of the drive motor control. The chosen opening positions are adjustable, i.e. the through opening of the valve can be increased or decreased by using water supply control (17).
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