In this paper, we present a geometrical model to calculate the radiation reflected from an external reflector inclined backwards and then absorbed onto a basin liner of a basin type still. The effect of the inclination of the external reflector on the distillate productivity of the still with both the internal and external flat plate reflector on a summer solstice day at 30 degrees N was theoretically predicted. We found that the distillate productivity of the still can be increased by inclining the external reflector even in summer, but the augmentation is smaller than in winter. Further, the benefit of both the internal and the inclined external reflectors of the basin type still would be considerably less in summer than in winter.