Two solar-stills (single basin and double decker) were fully fabricated and tested at the Campus of the University of Bahrain. Both stills have the same basin area. The inner dimensions of each were 90 x 50 cm (effective area is 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 glass cover temperature, the chamber temperature, the water temperature and the ambient-air temperature. The hourly amount of extracted distilled water, the various temperatures and the insolation were monitored for a five-month period (February-June). Two types of measurements were performed; one with still-sides insulation and the other without. It was found that the monthly average amount of the total daily-distilled water production was highest in June for both types of stills. This is expected, since 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 per day (3.91 l/m(2)/day), and in the non-sides insulation case the total daily amount was 1410 ml per day (3.13 l/m(2)/day). For the single-basin still, the June daily production was 1280 ml per day (2.84 l/m(2)/day) in the case of stills with sides insulation and 1105 ml (2.455 l/m(2)/day) in the case of no-side insulation. In February, March, April and May the average total daily productions were 1045, 1340, 1420 and 1630 ml per day in the case of stills with sides insulated and 843, 936, 1045 and 1180 ml per day in the case of no-side insulation of the double-basin still respectively. For the single-basin still, the production were 720, 765, 890 and 1010 ml per day in the case of stills with sides insulated respectively, and 655, 745, 810 and 945 ml in the case of no-side insulation respectively. These measurements reveal the following: (i) adding 2.5 cm of styrobore insulation material to the solar stills' sides causes a noticeable increase in water production; and (ii) the daily average still production for the double-basin still is around 40% higher than the production of the single-basin still. (C) 2003 Elsevier Ltd. All rights reserved.