A theoretical and an experimental model are presented of the transient and steady-state performance of two types of solar stills. Both a conventional and an external condenser-type still were constructed. The two stills were tested under the same conditions. Comparisons were made of productivity and efficiency under different conditions. The still productivity and efficiency were considerably greater for the external condenser-type still than for the conventional still. We found good agreement between measured and predicted values when using a numerical model.