A simple and efficient method for the behavior description of solar stills, developed on the basis of extensive testing, is theoretically and experimentally evaluated. The method relates the main climatic data and operating conditions of the still with distilled water output in daily and night base with linear equations using characteristic coefficients. Evaluation of the method is performed in three steps, the first being experimental determination of the coefficients and successive prediction of output, the second being calculation of coefficient values through analytical relations and the third being the use of the model in a continuous way. The agreement between the predicted and experimental water output and also between experimental and theoretical values of the characteristic parameters reveals the validity and suitability of the developed method. The results of the investigation show that this method is a valuable tool used not only for the optimization of the still in the design phase but also for evaluation of test results of an existing installation in order to further improve it.