A solar desalination system based on an innovative passive vacuum concept, utilizing low-grade solar heat, was studied experimentally. The system uses the natural means of gravity and atmospheric pressure to create a vacuum, under which liquid can be evaporated at much lower temperatures and with less energy than conventional techniques. A vacuum equivalent to 3.7 kPa (abs) or less can be created depending on the ambient temperature at which condensation will take place. The system consists of a heat source, an evaporator, a condenser, and injection, withdrawal and discharge pipes. The effect of various operating conditions (withdrawal rate, depth of water body and temperature of the heat source) were studied experimentally and compared with theoretical results. The experimental results agreed well with the theoretical predictions. It was found that the effects of withdrawal rate and the depth of water in the evaporator were small while the effect of heat source temperature was significant. (C) 2003 Published by Elsevier Ltd.