Usage of river, lake or underground water as heat source-sink in heat pump systems is rare in Turkey, in general, and in the city of Adana, in particular, which is situated 30 km inland from the north-eastern corner of the Mediterranean Sea. In this study, the possibility of using Seyhan River, which bisects Adana and Seyhan dam lake, as heat source-sink is investigated. The temperature of Seyhan River was monitored throughout the year and the data were compared with those of the ambient air. Analysis of the results of the experimental study carried out using a heat pump system that was capable of utilizing both air and water as heat source-sink revealed that the use of Seyhan River instead of ambient air could be advantageous during the whole heating and cooling seasons. (C) 2002 Elsevier Science Ltd. All rights reserved.