Abstarct: Desalinating the salt water, especially sea water is one of the permanent solution for low-water disaster. Common thermal water desalination like MSF and MED, are economically appropriate for high capacities of water production, and are not designed for the local usages. Using the heat losses of power plants as the main heat source of desalination is one of the most favorable mechanism for recent trends. But due to the lower electrical losses, small power plants for local use is of preference, since which the high reliability, lower harmonic losses, and environmental matters are satisfied as well. So, especial concern should be made for using heat losses of small power plants. HD water desalination which is designed baxsed on air vapor absorption at high temperature, is one of the recent trends of water desalination at low capacities. This mechanism can use sun radiation and other heat losses. In this study, a type of HD water desalination with open air cycle in which the exhaust heat losses of a 3-MW gas turbine is used as a heat source, is modeled. After a great review of pervious work, the basic equation of the main part of humidification and dehumidification are derived and programmed in MATLAB. After that, the model is analyzed parametrically and the performance of the water desalination is investigated. Parametric analyzed proves the necessity of economic model to be lixnked to the baxse model, in order to have optimized design parameters. Therefore, by lixnking the economizer model to the baxse model and determining the cost function, the optimization process is done using genetic algorithm toolbox of MATLAB. For the optimized design, the final cost of each cubic meter water was 0.6 US dollars. At the final, a comparison is made for all water desalination mechanism, which proves the high potential of HD technique to be combined with the low power generators.