In a gravity fed cooling tower liquid return system having a common header with a plurality of valved sub-headers, a distributive control system, risers on the sub-headers, and sensor/transmitters on the risers, some of the sensor/transmitters controlling the valves on their respective sub-headers, sensing the liquid level in each of the sub-headers, comparing the sensed liquid levels in the distributive control system, and controlling the liquid levels in the sub-headers in response to the sensed liquid levels.