Apparatus for treating water has a container having a clarification zone, a water entry arrangement for flowing water into the clarification zone, and water exit units mounted to the container for at least partial immersion in the water in the clarification zone. Each water exit unit has a transfer channel for transferring a flow of clarified water from a layer of the water to a predetermined depth in the clarification zone and to direct the received clarified water to a water exit arrangement. A height adjustment mechanism is used for differentially adjusting the heights of the water exit units and their transfer channels relative to the container so as to compensate for any angular tilt of the container owing to the container being deployed on sloping ground.