Abstract: This invention relates to an apparatus for the desalination of sea water or brine. The apparatus comprises one or more vertical columns divided into a number of cylindrical portions. Each portion constitutes one stage comprising one or more film evaporators formed by vertical tubes, a single brine collection tank of circular section provided with upper lateral apertures, a throttle system, one or more syphon tubes and one or more preheaters having vertical tubes expanded into the same tube plates as the vertical tubes of the film evaporators. The apparatus also comprises pipes and water boxes located inside the tanks for connecting the preheaters of the several stages, connecting pipes between the stages and a final tube bundle condenser positioned below the last stage.