The characteristic equation has been used for experimental results of a passive solar still to generate linear and non-linear characteristic equations for winter and summer conditions. The different angles of inclination of condensing cover (15 degrees, 30 degrees, 45 degrees) have been chosen for winter and summer conditions both. It has been observed that the passive solar still with inclination of 45 degrees gives better performance both in winter and summer respectively. Different water depths (0.04, 0.08, 0.12, and 0.16 m) have also been taken for solar still with 30 degrees inclination angle for summer weather condition. Comparisons of instantaneous gain and loss efficiencies at 0.01 and 0.04 m water depths for a 15 degrees inclination angle have also been made to show the effect of water depth on the performance of solar stills. It was found that a lower water depth gives better efficiency, which is in agreement with many investigators. The instantaneous gain and loss efficiency curves have been simultaneously analyzed to give a better understanding of the performance of solar stills. The proposed method will be used to standardize the design and operational parameter of a passive solar still, i.e. angle of inclination and water depth for highest yield for a given climatic condition.