Heat pump systems have been widely used in buildings and industries due to their high performance. In this study, a leaving water temperature control scheme has been proposed for a water-to-water heat pump for hot water supply. The study was focused on the following four schemes: (1) using an auxiliary electric heater, (2) varying compressor speed, (3) adjusting water flow rate, and (4) adding heat to the secondary fluid flow of the heat source. With schemes (2) and (3), the system showed higher performance than other schemes. However, scheme (2) could not attain the appropriate LWT at low EWT heat source conditions. For all EWT conditions, using schemes (3) and (4) enabled the system to reach an appropriate LWT. Scheme (4) can be adopted as the best technology to control LWT, because it is not easy to vary flow rate of the secondary fluid as in scheme (3). (C) 2012 Elsevier Ltd. All rights reserved.