Abstract: A water storage tank is formed by a plurality of curved wall sections adapted to be secured together to form a circular tank. A ground mat is placed on the ground and extends outwardly of the tank wall. A plurality of hold down members are placed at the inside juncture of the tank wall and ground mat. A flooring sheet overlaps the ground mat and extends up and over the side wall of the tank and is clamped to an upper portion of the wall. A tubular fitting extends through a lower portion of the side wall to provide an inlet and outlet for water.