Water-cooled air-conditioning systems (WACS) are, in general, more energy efficient than air-cooled air-conditioning systems (AACS). The Laws of Hong Kong prohibit the use of fresh water from town mains for comfort air-conditioning, which rules out the use of cooling towers to most air-conditioned buildings. In the absence of lakes or major rivers in Hong Kong, only those buildings that are situated near the harbor can adopt WACS. As a measure to cut down greenhouse gases emissions, the Hong Kong Government is currently exploring the feasibility and viability of widening the use of WACS by the provision of centralized, district-wide water supply systems, which include seawater supply systems for once-through condenser cooling or for making up of water losses at cooling towers, and district cooling systems. Evaluation of the likely energy, economic and environmental benefits of such capital-intensive infrastructure developments requires estimation of the simultaneous cooling demand of a large group of buildings on a district scale, and the energy use for air-conditioning such buildings. This paper describes the method used in these estimations. Comparisons of the results estimated by this method with results obtained by detailed simulation, and with building energy use data obtained from surveys and audits are presented. (C) 2001 Elsevier Science B.V. All rights reserved.