An irrigator has a single irrigation arm adapted to move in reciprocal rotational motion. In a first setting, the irrigator sprays irrigating liquid at a first orientation with respect to the arm to move the arm in a first direction. In a second setting, the irrigator sprays irrigating liquid at a second orientation with respect to the arm to effect a reversal in the rotational direction of the arm. Alternating mechanisms are provided to alter the arm between the first and second settings.