A theoretical and experimental study was carried out to investigate the effect of adding a passive condenser on the performance of the single slope, basin type solar still. A theoretical model based on Dunkle [1] mass transfer (evaporation) rate was developed. The model assumes that the transfer of water vapour from the still to the condenser is due to one or more of the following mass transfer modes; (i) diffusion, (ii) purging and (iii) natural circulation. The theoretical results indicate that diffusion contribution is relatively small. The contribution through purging represents the fraction [V(cond)/(V(cond) + V(s))] of the still yield, while it represents 75% of the still yield through natural circulation. An experimental study that simulates the purging mass transfer mode was investigated. The experimental results show good agreement with the theoretical predictions and an increase of 45% in solar still efficiency was obtained.