This study investigates experimentally and analytically the natural cooling of water at night in an uninsulated open tank by evaporation, convection and sky radiation in hot and areas. In addition, the feasibility of using the obtained cooled water for human thermal comfort inside buildings is studied. The experimental results showed that for a tank having an open surface area of 1 m(2) and a depth of 0.5 m, by the ends of nights, the water temperature values ranged from 17.2 to 18.9 degrees C, while at the beginnings of nights, the water temperatures ranged from 23.8 to 27.1 degrees C. The evaporative and convective mass transfer cooling portions ranged from 38.7% to 57.4% of the total net cooling. The percentage of water lost from the tank, including the evaporated convective mass transfer cooling portions at different nights ranged from 2.5% to 4.13%. The model results were validated by measured values and good agreement prevailed. The analytical results showed that as the water depth in the open tank varied from 0.2 to 0.6 m, the net cooling of the water ranged from 10.53 to 19.7 MJ/m(2) with temperature values ranging from 14.3 to 18.7 degrees C. The results indicate that the naturally cooled water final temperature and cooling energy results are feasible for use for human thermal comfort inside buildings through radiant ceiling cooling panels systems in hot and areas. (c) 2006 Elsevier Ltd. All rights reserved.