Abstract: A thermocompression apparatus for desalting saline water, wherein: the evaporator tubes extend vertically above the separating chamber for steam and non-evaporated water and have their lower ends opening into the separating chamber through a lower header plate; the upper ends of the evaporator tubes extend through an upper header plate into a plenum chamber overlying the latter, said plenum chamber being arranged to provide a pool of saline water submerging the upper ends of the evaporator tubes; and each of said upper ends having means therein arranged to receive saline water from the pool and to discharge it in the form of falling film on the inner surface of its respective evaporator tube, whereby the said film and the steam produced therefrom flow co-currently downwardly in the tubes towards the separating chamber.