Iran has a considerable amount of gas turbine plants and many of them have been located in the south, near the seashore region. Because of fresh water shortage in some parts of Iran, these power plants are used for supplying fresh water. The most common desalination methods are RO (Reverse Osmosis), MSF (Multi-Stage Flash distillation), MED (Multi-Effect Distillation), and MED–TVC (Multi-Effect Distillation-Thermal Vapor Compression). In this research, methods of RO, MED, and MED–TVC are compared. Simulation results show that heat recovery of emissions of the main stack is an optimal case for providing demineralized water (DM) required for injected steam of MED desalination. This subject is very important because of improving thermal efficiency of power plant using extra heat recovery. It has been shown too that by adding three rows of finned tube to de-aerator evaporator, which is very simple and low cost, required steam for generating 5200 m3/day of desalinated water is obtainable.