In this experimental work, the effect of cotton bags filled with phosphate on solar distillery performance has been investigated. In this study, 25 phosphate bags are evenly distributed (5 × 5) with a length equal to 50 cm in a wooden box called the modified solar still (MSS). This system was compared with the conventional solar still (CSS) in the same climatic conditions. Phosphate bags are placed vertically to increase the energy storage capacity, and the water's surface area since the capillaries inside the phosphate bags play an important role in increasing the energy storage capacity. Experiments were conducted at El Oued University in Algeria during April and May 2020, with 1 cm and 2 cm of saltwater depth. The cumulative yield of 5.27 and 4.87 kg was produced from the MSS at 1 cm and 2 cm of saltwater, respectively, while the cumulative yield of the CSS was 3.8 kg. The MSS's overall efficiency at 1 cm and 2 cm of saltwater was enhanced by 28 and 22.5%, respectively compared with the CSS. The presence of calcium and copper in phosphate stores the heat energy during morning and afternoon, and stored heat energy was released during evening. Finally, it can be concluded that increasing phosphate bags significantly enhances the productivity in solar distillation, increasing efficiency and productivity.