Abstract: A water collection trough has an edge arranged in the plane of a roof and a bottom, arranged with spacing from the edge, with an opening. The opening leads to a drainage pipe mounted down at the bottom of the trough. Two parallel plates are arranged spaced apart, a lower plate being fixed in the water collection trough and an upper plate being fixed above the edge of the water collection trough. The edge of the upper plate projects beyond the edge of the water collection trough in such a way that, to form a closed flow in the drainage pipe. The water to be led away is accelerated ahead of the edge of the water collection trough and, after a two-fold deflection of about 90.degree. in each case, ahead of the opening in the bottom.