From the experimental and theoretical investigations, it was observed that using a weir on the edge of each step of the stills leads to even distribution of water onto the RN 1 surface and increases the residence time. It is suggested that the convective heat transfer coefficient, very important parameter in the still modeling, should be determined from the produced experimental data for different still geometries and operational conditions. It was also found that increasing the level of water on the evaporation surface and decreasing the air gap in the still lead to decrease and slightly increase in the total productivity of the still, respectively. It was concluded that the still with PCM is superior in productivity compared with still without PCM by about 31%. The daily productivity was theoretically obtained about 6.7 and 5.1 kg/m2/day for still with and without PCM, respectively. The overall thermal efficiency of the still with PCM was 64% and for still without PCM was 47%.