Basin-type, multiple-effect, diffusion-coupled solar stills consisting of a tilted double glass cover, a horizontal basin liner and a number of closely spaced vertical partitions in contact with saline-soaked wicks were constructed and then examined in an outdoor experiment in fall and winter at Okinawa, Japan. This new type of still is greatly improved by narrowing diffusion gaps between the partitions, increasing the number of partitions, sandwiching small spacers between partitions and insulating the frame of the glass cover. The daily performances of the improved still are in good agreement with predictions calculated from the theoretical model developed by Tanaka et al. [1]. The still with 5-mm diffusion gaps between 11 partitions produces 14.8-18.7 kg/d distillate per unit effective area of the glass cover at 20.9-22.4 MJ m(-2) d(-1) solar radiations incident on the glass cover and 19-30degreesC ambient air temperatures and is highly productive in comparison with the 7-effect diffusion-type still with 8-mm gaps developed by Okamura et al. [2] and the 3-effect diffusion-type still with 19-mm gaps of Cooper and Appleyard [3].