This paper presents the simulation and the experimental validation of the distillation module of a desalination unit, currently operating in Sfax, Tunisia. The desalination process is based on the Solar Multiple Condensation Evaporation Cycle (SMCEC) principle. The work presented in this paper focuses on modelling the desalination module as it is supplied with either water heated by solar energy or geothermal water. Geothermal water resources are abundant in Tunisia with salinity levels of 1-50 g/l. The simulation of the dynamic behaviour of the desalination module with and without disturbances on the inlet temperature was carried out to predict the variations of key output variables subjected to thermal variations. Such variables include water temperature, air temperature, humidity in the evaporation and condensation chambers and the amount of produced distilled water. To validate the dynamic model of the distillation module, a series of experiments was conducted. Experimental results were compared with the simulation results. It was shown that the developed model is able to predict accurately the trends of the heat and mass characteristics of the evaporation and condensation chambers. As a result, the proposed model can be used to design and test the behaviour of such a type of desalination unit. (C) 2003 Elsevier Ltd. All rights reserved.