The current work reports a numerical investigation of the water produced and thermal performance of a solar still (SS). Using a SS for desalination is a proposal for low-income remote communities needing potable water. The study deals with the SS under five different concentrations of salt (0, 5, 10, 20, and 35 g/kg). Previous experimental results reported in the literature indicate that the increase in salinity leads to a decrease in productivity, so phase change material (PCM) was added under the water basin to counter the reduction. The mathematical model and numerical methodology were validated by comparing them with experimental results reported in the literature. The relative difference between temperatures was less than 2%, and for water production, it was less than 3.5%. The present mathematical model has the novelty of utilizing the water properties as a function of temperature and salt concentration, contrary to other models that use pure water properties. The results show that daily productivity decreases when the salinity increases from 0 to 35 g/kg. For each case, the time evolution of hourly and cumulate productivity is presented, as well as water temperature and the temperature difference between water and glass. Also, the behavior of heat flux between water and PCM is analyzed. The overall efficiency is calculated for all the cases.