The photovoltaic and thermal performances of a photovoltaic-thermal (PVT) collector with water heating in buildings are presented in given climate conditions. According to energy balance equations, some performance parameters can be determined, including the photovoltaic efficiency, the temperature of solar cell and the outlet temperature of water, as well as the photovoltaic power and heat transfer rate. The influences of the series-connected PVT module number, the inlet temperature of water and the mass flow rate of water on the photovoltaic and thermal performances were discussed and analyzed. The approaches of improving the photovoltaic and thermal performances were concluded. The results indicated that the less series-connected PV modules, the lower inlet temperature of water and the higher mass flow rate of water resulted in the high photovoltaic efficiency. (C) 2013 Elsevier B.V. All rights reserved.