Abstract: A distribution system for a water cooling tower directs incoming hot water to particular regions of a fill assembly which are determined by the magnitude of the hot water flow rate, and structure is provided for maintaining an equal head of water above all of the nozzles in current operation. During periods of relatively low flows, a weir member mounted within a distribution box of the system directs all of the incoming hot water to an outer distribution zone which is located over four outer regions of the fill assembly. Once the hot water flow rate is increased above as certain, predetermined value, a portion of the water spills over the weir and is conveyed to an inner distribution zone located over a central region of the fill structure while the remaining portion of the water is directed toward the outer zone so that water is directed to the entire horizontal area of the fill structure.