Abstract: A liquidtight tank or reservoir, made of generally prestressed reinforced concrete, particularly for purification plants, comprising a plurality of plane plates which are connectable to each other and comprise substantially a central portion and a hammer-shaped element disposed at each of the two ends is described. Between two said hammer-shaped elements belonging to two consecutive plane plates which are approached to each other at the moment of the assembly there is interposed a connection element so that said two consecutive plane plates are connected to each other forming an angle which depends on the dimensions and shape of said connection element.