A process and system for obtaining fresh water from salt water such as sea water, by direct contact heat transfer using staged evaporator-condenser units operating with a low boiling water-immiscible liquid hydrocarbon. Each stage comprises a closed vessel divided into two compartments, an evaporator and a condenser, by a bubble cap tray similar in construction to those used in distillation. Relatively hot fresh water is introduced into the liquid hydrocarbon contained in the lower compartment of each stage, causing boiling of the hydrocarbon at a temperature differnce of 2.degree.-4.degree. F. Hydrocarbon vapors pass from the evaporator compartment through the bubble caps to the upper condenser compartment where they are condensed in contact with a colder saline stream, and the condensed hydrocarbon is returned to the lower compartment. The heated saline stream is flash evaporated and the vapors are condensed in direct contact with recycled fresh water from the evaporator compartments, and a portion of this combined stream is taken off as product, the remainder of the combined stream being further heated and reintroduced into the evaporator compartments of the staged units. Sea water feed is introduced into the condenser compartment of the last stage and passes into the respective condenser compartments of each of the preceding stages, and is further heated therein in each stage, and the hot fresh water introduced into the evaporator compartment of the first stage is passed through the evaporator compartments of each succssive stage and is further cooled in each successive stage.