Abstract: A water vessel is assembled from a number of vessel units having at least one connecting opening, a short tube portion formed at each connecting opening of the vessel units, a connecting flange formed at an end of each short tube portion, and an annular packing interposed between contact surfaces of the connecting flanges of an adjacent pair of vessel units and received by annular recesses of the contact surfaces. A number of connecting members are arranged around each pair of connecting flanges of adjacent vessel units with the pair of flanges being inserted into grooves formed in the connecting members. The pair of flanges are pressed into contact by bolts for clamping the end portions of the connecting members together and utilizing wedge action between peripheral wedge portions of the pairs of flanges and groove wedge portions of the connecting members.