In and and semi-arid regions the lack of drinkable water often corresponds with high solar insolation. These conditions are favourable for the use of solar energy as the driving force for water treatment systems. Especially in remote rural areas with low infrastructure and without connection to a grid, small-scale, stand-alone operating systems for the desalination of brackish water from wells or saltwater from the sea are desirable to provide settlements with clean potable water. Fraunhofer ISE is currently developing a solar thermally driven stand-alone desalination system. The aim is to develop systems for a capacity ranging from 0.2 to 20 m(3)/d. Technical simplicity, long maintenance-free operation periods and high-quality potable water output are the very important aims which will enable successful application of the systems. The separation technique on which the system is based is membrane distillation. The implemented heat source is a corrosion-free, seawater-resistant, thermal collector or a standard flat-plate or vacuum tube collector coupled with a corrosion-free heat exchanger. Laboratory tests under defined testing conditions of all components are very important for the preparation of successful field tests under real conditions.