A system for draining water from a roof or partial roof construction with flat or low- sloped construction, the system comprising a vertically upright restrictor (12,13) comprising a hollow conduit located at a lowest point in said roof or partial roof construction for draining water from said roof, said restrictor (12,13) including at least one apertures (16) for limiting or restricting the transportation of water to drainage pipes through said aperture(s) (16), said aperture(s) (16) defining the maximum water flow of the water mass collected by said roof, and wherein at least one of the aperture(s) (16) is/are present in the form of at least one triangular aperture with its apex pointing upwards is placed on the drainage pipes of the roof of a building for preventing overload of the local water removal and/or sewer system.
