Computational fluid dynamics simulations for water desalination using forward osmosis were conducted on a flat membrane module. In the simulations, the effect of the porous support layer is assumed negligible. The simulations were performed with two values of flow rate such that the Reynolds number equals 200 and 800 in each channel. The working temperatures of both the feed and the draw solutions were varied from 20°C to 40°C. The feed solution had a concentration of 0.00355 solute mass fraction while the draw concentration was set to 0.0355 solute mass fraction. In all simulations, the laminar model was utilized. The results of the simulations suggest that the osmotic pressure is not the only factor that affects the water flux in forward osmosis when there is a temperature difference between the two sides of the membrane. The solution properties have a significant effect on the separation process. As the solution temperature increases, the viscosity decreases, which in turn increases the water permeation through the membrane. The feed temperature had a more substantial influence on the water flux compared to the draw temperature. Also, the effect of changing the flow rate did not change the results substantially.