Membrane distillation (MD) is a thermally driven membrane process in which a hydrophobic microporous membrane separates a hot and cold stream of water (e.g., [15,16]). The hydrophobic nature of the membrane prevents the passage of liquid water through the pores while allowing the passage of water vapour (Fig. 1). The temperature difference produces a vapour pressure gradient which causes water vapour to pass through the membrane and condense on the colder surface. The result is a distillate of very high purity which, unlike in conventional distillation, does not suffer from the entrainment of species which are nonvolatile. For desalination processes, the seawater