The present invention relates to a device comprising a coherent manmade vitreous fibre substrate (MMVF substrate) and at least one first conduit (2) and at least one second conduit (3), each conduit having first and second open ends, wherein the MMVF substrate (1) comprises man-made vitreous fibres bonded with a cured binder composition, wherein the first open end of the first conduit and the first open end of the second conduit are each independently in fluid communication with the MMVF substrate, wherein the first conduit is at a greater height than the second conduit, wherein at least a portion of the MMVF substrate is disposed between the first and second conduits. The MMVF substrate provides for an increased water storage ability due to the hydrophilic behaviour of the substrate and its increased surface.