Solar distillation literature reports a generalized use of stills with single and double slope condensing covers, where modeling equations describe a solution approach that considers the condenser as a single element. The solution for a double slope still analysis is generally forced to the case of one with a single flat condensing cover. This paper proposes a new lumped parameters mathematical model to study the asymmetries that arise in the temperature and distillate yield in double slope solar stills. The condenser is studied as a two-element system and non-simplified equations for heat transfer and optical transmission characteristics are used. The model is tested for the case with the strongest thermal differences and validated with experimental data. Overall results show a good correlation between predictions and experimentation. (C) 2003 Elsevier Ltd. All rights reserved.