In this experimental study, an attempt has been made to store excess heat energy in solar stills during the daytime for the continuation of the process at late evening and night hours. To investigate the effect of energy storage materials on the productivity under the same climatic conditions, two identical solar still units are fabricated with an effective area of 0.5 m(2). The performance of the still is examined with various energy storage materials, like black granite gravels, pebbles, blue metal stone, and paraffin wax. It is concluded that (i) the energy storage materials in the still store a considerable amount of heat during noon hours and release the stored heat to the basin water in the late evening and night hours, and (ii) black granite gravels are more efficient than pebbles and blue metal stone when used as energy storage materials.