The Bavarian Center of Applied Energy Research (ZAE Bayern) and T.A.S. GmbH & Co. KG, Munich, have optimized a distillation method which was originally developed at the at the University of Munich and which is protected by patent. The method -developed for small-scale production (0.5-2 m(3)/d) - is ideally suited for the use at decentralized stand-alone operation because it is nearly maintenance free and needs no electrical grid connection. It can be run either by solar energy or by waste heat from a diesel generator. The thermodynamic principle of multi-effect humidification (MEH) is based on the evaporation and condensation of water inside a thermally insulated box at ambient pressure. Air transports water vapour from the evaporator to the condenser where the distilled water is collected. A very efficient construction of evaporator and condenser allows high heat recovery ratios. The gained output ratio (GOR) (performance ratio) quantifies the multiplicity of thermal energy use for evaporation of the brine in the MEH system compared with evaporation without heat recovery. The process has been technically optimized so that the air circulation is driven entirely by natural convection. The produced distillate is of pure water quality. In order to make the proven reliable desalination process needing low maintenance competitive from economic point of view, 24-h operation of the desalination system is necessary. Thus, if the system is driven solar thermally, a thermal storage tank has to be implemented.