In this paper, a cascade solar still (CSS) was designed for water purification with a view of enhancing the daily productivity. The work studied the influence of water flow rate on the internal heat and mass transfer and daily productivity of CSS. Dunkle's relation was employed to predict the still behavior because of its wide application in the literature. However, Dunkle relation could not satisfy our CSS behavior due to the special geometry and operational conditions. Therefore, the internal heat and mass transfer coefficients were determined using the experimental data obtained from the modified cascade solar still designed in this work. The results showed a decrease in the internal heat and mass transfer rates as well as daily productivity with an increase in water flow rate. In this regard, the daily productivity was found to be 7.4 and 4.3 kg/m(2)day, for minimum and maximum flow rates, respectively. (C) 2010 Elsevier B.V. All rights reserved.