A mathematical model is developed to investigate the potential of the membrane distillation process to be a stand-alone process. The model includes internal heat recovery and relates the major cost parameters to the heat and mass transfer of the process. The cost parameters are the energy required for heating, the energy required for pumping, and the specific membrane area. It was found that the permeability of membrane distillation system (defined below) for the modules available in the literature is in the range of (1)10(-8) to (1.5)10(-6). Taking the upper limit, it was found that for membrane distillation system to become competitive for seawater desalination, the feed solution need to be discharged at temperature over 50 degrees C and so a low-grade energy is needed. Moreover, it can be concluded that the process is closer to be economic when Reynolds number is in the range 3000-5000 (transition from laminar to turbulent flow).