Abstract: A runner extending from a blast furnace to a slag pit, water spray unit for manufacturing granulated slag or slag ladle is partly or wholly composed of a plurality of trough elements each made from copper or copper alloy. Each trough element comprises a hollow body having an inner space which is divided into sections by a plurality of partitions to define throughout the inner space of the body a series of passages in which a cooling medium is allowed to flow without stagnation. The cooling medium within the hollow body of the trough element is introduced under a predetermined pressure from a pipe line for supplying cooling medium into the body, whereby the cooling medium freely flows at a relatively high velocity in the passages defined by the partitions and molten slag glowing in contact with the surface of the trough element is cooled to a desired temperature which prevents wear and loss of the element and makes it possible to produce hard granulated slag from the molten slag.