The shortage of drinkable water in many areas of the world represents a fatal problem. The desalination of saltwater can be a solution to this problem. Solar still is a simple and reliable system to be used in arid and sunny regions, but it has the disadvantage of relatively low productivity. A new configuration of solar still, namely single slope double basin solar still, is proposed in the current work to increase productivity. A prototype of this still type was designed, fabricated, and tested. Besides, a multi-phase, three-dimensional CFD model for mass and heat transfer under unsteady conditions of such still type using CFD ANSYS was developed. This model enabled predicting the performance of this still configuration. The simulation results were validated with experimental data for the climate conditions of Shebin El-Kom, Egypt (latitude 30.5° N and longitude 31.01° E). Within the scope of this study, simulation results were found to be in good agreement with the experimental data. The daily simulated and experimental accumulated productivities of the single slope double basin solar still were found to be 3.148 lit/m2 and 2.855 lit/m2 for a water-/equivalent water depth of 2cm. Also, the simulated and experimental daily efficiencies were around 27.65% and 25%, respectively for the tested water-/ equivalent water depth, whereas the reported highest efficiency of the conventional single-slope single basin solar still is 15.5%.