Two solar stills (single basin and double decker) were fabricated and tested. Both have the same basin area. The inner dimensions of each was 90 x 50 cm (effective area 0.45 m 2). For the double-decker basin solar still, the upper glass cover and the first basin were tilted at 12degrees with respect to the horizontal, while for the single basin solar still, the glass cover was tilted at 36degrees with respect to the horizontal. Several copper-constantan thermocouples were installed in both stills to measure the temperatures of the glass cover, the chamber, the water and the ambient-air. The hourly amount of extracted distilled water, the various temperatures and the insolation were monitored for a 5-month period (February-->June). Two types of measurements were performed; one with the still-sides insulated and the other without. The monthly average total daily-distilled water production was highest in June for both types of stills because the insolation during this month is higher than that in any other month during the testing period. For the double-basin still, with sides insulated, the June production was 1760 ml/day (3.91 l/m(2)/day), and, for the sides not insulated case, the total daily amount was 1410 ml/day (3.13 l/m(2)/day). For the single-basin still, the June daily production was 1280 ml/day (2.84 l/m(2)/day) in the case of the still with sides insulated and 1105 ml (2.455 l/m(2)/day) for the sides not insulated. In February, March, April and May, the average total daily productions were 1045, 1340, 1420 and 1630 ml/day in the case of stills with insulated sides and 843, 936, 1045 and 1180 ml/day in the case with the sides not insulated for the double-basin still respectively. For the single-basin still, the production was 720, 765, 890 and 1010 ml/day in the case of stills with insulated sides, respectively, and 655, 745, 8 10 and 945 ml in the case of sides not insulated, respectively. Adding 2.5 cm of styrobore insulation material to the solar stills' sides causes a noticeable increase in its rate of water production. The daily average still production for the double-basin still is around 40% higher than the production of the single-basin still. (C) 2004 Elsevier Ltd. All rights reserved.