Abstract: A roof drain system in which an air duct is mounted on a building to extend along the lower edge of the roof to have the water from the roof flow thereover, a blower communicates with the air duct to supply air under above atomspheric pressure thereto, and the duct has apertures along the length thereof for passing air in jets directed laterally outwardly of the building to substantially disrupt the water into droplets as it flows across the air duct and thereby distribute the droplets in a wide band outwardly of the roof line of the building. Apparatus for automatically operating the blower means when it rains, is advantageously provided.