configuration having a top wall 44 in a common generally horizontal plane with the top wall 25 of the housing 12 inclined sidewalls 45 and front and rear end walls 46 and 47 the tank 40 being of a width corresponding to that of the housing 12 for the system proper the tank 40 is hermetically sealed and securely anchored to the roof by suitable means and has a pump 50 with a water supply line 52 extending from the tank 40 through the front end wall 46 and the rear end wall 27 of the housing 12 for connection to the distribution pipes 34 as best seen from fig4 a pair of water recovery troughs 54 are aligned in tandem with the troughs 32 each being connected by a drain line 56 to one of the troughs 32 to permit excess water to flow by gravity from the troughs 32 into the troughs 54 the troughs 54 are preferably inset into the roof in a manner similar to that of the troughs 32 so as to be disposed beneath the roof line but isolated from the upper circulating tank 40 a sump pump 58 is disposed in each of the troughs 54 and has a discharge line 60 extending upwardly into the tank 40 a float valve 62 senses the water level in the tank and activates the sump pumps to deliver water into the tank from the troughs 54 when the water in the tank 40 drops below a predetermined level a modified form of evaporator section is illustrated in fig5 for use with the novel and improved system of the present invention and specifically wherein the location of the coils 14 and filter blocks 15 are reversed or interchanged with respect to the blowers.