The invention relates to a device for forming cavities in the ground for water drainage and/or water storage. Said device comprises a cube- or cuboid-shaped installation body (10), which has a front side (42) and an opposite back side (44), a top side (20) and an opposite bottom side (18), and two opposite lateral sides (22). The front side (42), the back side (44), the top side (20), the bottom side (18), and the lateral sides (22) have strand elements (14) arranged parallel or substantially parallel to each other. In the corner regions of the installation body (10) between the top or bottom side (20, 18) and one of the lateral sides (22), corner connecting elements (12) for the insertion connection of the strand elements (14) of the top side (20) or of the bottom side (18) to the strand elements of the lateral side (22) are arranged.