Hot climate countries require large amounts of desalinated water. The Reverse osmosis (RO) technique is currently considered the most reliable technique for brackish water and seawater desalination. However, its power consumption is considerably higher than all other techniques. Therefore, the present study investigates the performance of reverse osmosis plants in hot climate conditions. A typical Reverse osmosis system was designed, constructed and investigated. The ROSA software was also used for the analysis of seven different membrane elements. The experimental data were utilized in order to validate the simulation results of the ROSA software. A variance-based sensitivity analysis was performed in order to define the most effective design and operating parameters. The present investigation shows that the tap and brackish water membrane elements are more sensitive to the feed water temperature rather than the feed water pressure and concentration. Meanwhile, seawater membrane elements are more affected by the feed concentration. The detailed investigation of the different membrane elements shows that wastewater reclamation using reverse osmosis technology could be a significant source of low-cost fresh water for hot climate countries.