The aim of this study is to investigate theoretically the effect of different system operating conditions, types of air heater, and some different design parameters and a weather condition on a solar water desalination system performance under the climatological conditions of Ankara (40 degrees N,33 degrees E), Turkey. For this purpose, a computer simulation program based on the mathematical model is developed by means of MATLAB software. In this simulation program, the fourth order Runge-Kutta method is used to solve the energy balance equations numerically. The desalination unit is configured by a double-pass flat plate solar air heater with two glass covers, humidifying tower, storage tank and dehumidifying exchanger. The system used in this work is based on the idea of closed water and open air cycles. Air is heated by using a double-pass solar air heater whereas water is not heated.