In the present paper a study is conducted of the mass and heat transfer phenomena which rule the function of a direct evaporative cooler. A comprehensive mathematical model is developed, which is based on the latent and sensible heat transfer and can predict the efficiency of such a cooler under any circumstances of operation and water supply. As a development of the existing simulation models of direct evaporative coolers, the model presented here is general, as far as the temperature of the supply water is concerned as an independent parameter. In addition, direct evaporative cooling is evaluated according to its efficiency, the quality of produced air and the specific consumption of water while working in Mediterranean climates.