The clean water and energy are both the most important needs of mankind. The increasing population and the necessity to meet the need for freshwater requirements make the desalination process a popular topic. The reverse osmosis is one of the most popular technique for desalination. The main advantages of the reverse osmosis over other desalination techniques are the lower energy consumption and the robustness to the salinity of feedwater. The ambient conditions are the key parameters affecting the efficiency of desalination process. On the other hand, the design parameters of a reverse osmosis desalination plant also play an important role in the process. In this paper, both ambient conditions and the design parameters are investigated. The contributions of the study are to determine variation the specific power consumption and related total power requirement of single stage reverse osmosis desalination plant model with the ambient conditions and design parameters. The effects of design parameters and ambient conditions for power requirements are given in the results section. The simulation studies are performed at constant production rate in order to see the effects of each parameter to product properties. The increase in seawater temperature for constant seawater salinity decreases the power consumption while increasing the salinity of final product. The results indicated that design parameters should be optimized according to the size of the designed system and salinity of feedwater. Also, a case study is performed for a point at Marmara Region, Turkey.