Water tank and method for manufacturing a water tank

A water tank made from plastic material, which water tank is to be joined from at least two open identical injection molded or injected molded and embossed tank parts, the tank parts having opening edge structures matching each other in a joining plane of the water tank, each opening edge structure having a flat inner opening edge continuing a wall of the tank part, a sealing receiving channel for a sealing means, the sealing receiving channel being open towards the joining plane, and an outer flat opening edge continuing a wall of the sealing receiving channel, the opening edges being aligned with each other in the joining plane in joined condition of the water tank and being inner and outer fitting surfaces respectively with a width exceeding the thickness of the wall of the tank part and the wall of the sealing receiving channel by at least about one half, the opening edge structures being designed such that the water tank is to be assembled in a separable watertight tank version by local releasable clamping joining of the opening edge structures, wherein the water tank at least substantially has a shape of a hollow cylinder consisting of substantially semi-cylindrical tank parts each having outwardly rounded end caps, wherein a cylinder axis is situated in the joining plane, ribs in each tank part being arranged parallel to each other in both end caps and in the semi-cylindrical parts with the ribs formed in the end caps terminating with a respective distance from the first and last ribs of the semi-cylindrical parts, and wherein the ribs are tapering inwardly and define at each rib end a closed, substantially trapezoidal or triangular cross-section within the opening edge structure, wherein an extension of the inner fitting surface defined by each rib end has a shape of a closed strip following a shape of the rib cross-section and having substantially constant width, the edge strip surrounding a recess which is set back in relation to the joining plane, and wherein an insertion socket for inserting a centering member is formed in the recesses of the rib ends of at least some of the ribs.