System for draining water from a roof or partial roof construction with flat or lowsloped construction, the system comprising a vertically upright restrictor (9) comprising a hollow conduit located at a lowest point in said roof or partial roof construction for draining water from said roof, said restrictor (9) including at least one aperture(s) (12) for limiting or restricting the transportation of water to drainage pipes through said aperture(s) (12), said aperture(s) (12) defining the maximum water flow of the water mass collected by said roof.