In this study the heat transfer of air-water-vapour mixtures in a desalination plant using the aero-evapocondensation process was studied theoretically and experimentally. The present unit consists of a falling film evaporator and condenser made of polypropylene. It was designed to work at low temperatures (60-90 degrees C) using geothermal energy. A model for heat and mass transfer in the plant was developed, resulting in a set of classical equations. Two experimental pilot studies were used. The latter, installed, respectively, in France and the south of Tunisia, were supplied by fuel and geothermal energy. The influence of different thermal and hydrodynamic parameters on the unit performances was investigated. Experimental results were compared with the model presented showing that the model is well able to predict the trends of the heat and mass characteristics of the evaporator. In comparing the other desalination techniques, it was shown that in areas where geothermal water resources are available, the process is promising for cooling and for desalting geothermal water.