Abstract: The flow of water to an irrigation device, animal watering trough or other similar structure is controlled by a main valve which is operated by a water actuated mechanism. The water actuated mechanism includes an actuation container which is restrained to vertical motions and whose vertical motions are operatively connected to the main water valve. An off-time valve adjustably meters pressurized water into the container for controllable but very slow filling. When the container attains a predetermined weight, it moves downwardly against an upward acting force applied by the buoyancy of a surrounding fluid, bias means, counterbalance means, magnetic attraction or the like, moving the main valve open and allowing relatively large flows. The actuation container is latched in this valve opening position by suitable means such as contacting magnets. A venturi device connected to the container through an on-time valve is provided in the flow channel downstream from the main water valve.