Abstract: An underground water storage vessel includes a generally toroidal-shaped hollow body of rotationally moulded plastics with an upright turret having an access port therein. Formed on the outer surface of the hollow body are solid reinforcing ribs in a mesh-like pattern wherein the intersections between the ribs are integrally formed. The underground water storage vessels are installed in reactive soils with a cast concrete ballast extending from an upper region of the vessel via an aperture therein to an interface with a substantially incompressible material, the interface being located intermediate upper and lower regions of the vessel.