at least two caissons, wherein the height of each caisson is substantially equal to a vertical height of a hull of the floating production unit and extends, when mounted to the hull of the floating production unit, from a predetermined minimum distance from the bottom side of the hull up to at least the water-line during use, each caisson comprising an open top side and a through-opening in a bottom side;

a lift pump arranged inside each of the caissons and having an inlet at a vertical distance with a predetermined minimum submergence and adapted for pumping cold water from the caisson up to the floating production unit suitable for use as cooling medium by production equipment of the floating production unit; and

a sump tank, attached to the bottom side of each of the caissons such that each through-opening thereof is in fluid communication with a volume inside the sump tank, the sump tank being located between the bottom side of the hull and the at least two caissons when mounted and having a through-opening in a bottom side and being connectable to an upper end of a riser pipe, the sump tank being configured to hold a constant body of water;

and wherein the caissons have a width equal to the width of the sump tank divided by the at least two caissons connected thereto.