Abstract: In a clamping connection between a plastic water tank equipped with at least one flange and a heat-exchanger tube sheet carrying a deformable edge region, an elastic sealing device being retained therebetween under prestress, and the deformable edge region, before its deformation, extends parallel to the outer contour of the flange and, after its deformation to make the clamping connection, it has first partial regions deformed in an approximately wave-shaped manner over the flange of the plastic water tank, and non-deformed further partial regions extending parallel to the outer contour of the flange. The first partial regions deformed over the flange of the plastic water tank make a positive connection, in which the lower edges of the deformed first partial regions rest on the top side of the flange under prestress. To make deformation easier, the deformable first partial regions are cut free parallel to and at a distance from an outer edge at the height of the flange top edge.