Transformation of salty seawater into fresh water by the aid of solar energy is one of the solutions for overcoming the lack of these waters with an eco-friendly procedure. The use of solar stills is one of the solutions that use solar energy with a simple design to produce fresh water in small to moderate amounts. Hemispherical solar stills are one kind of still design that does not require a particle rotational orientation, and they have proved to be more efficient than traditional designs. Solar stills generally possess a low thermal efficiency, with limitations of working hours, i.e., only daytime. To overcome these problems, rocks placed in the saline water basin are used as heat storage materials to increase the working period of the design. In the present work, different amounts of river rocks are utilized to study the effect of this addition experimentally. Steady state tests are conducted to study the influence of these additive rocks on the enhancement of solar energy absorption, since increased working time is assured by published research. Two volumes of rocks (300 mL and 600 mL) were tested, and both increased water productivity, by 52% and 58%, respectively. The increases are explained by the increases in solar energy absorption, since steady state cases were used.