Efficiency of photovoltaic water pumping systems (PVPS) decreases remarkably as PV cells temperature rises, thus to improve the performance of such systems and their efficiency, PV cells temperature should be kept as low as possible. In this research, a PVPS with collectors installed beneath the panels was used to cool down the PV cells. Pumped water by the solar pump is divided into two parts: the first part joins the second one after passing through the collectors installed beneath the panels and flows to the outlet. The second part passing through the collectors cools down the PV panels and therefore increases the efficiency of PVPS. Effect of flow of water through these collectors on PV cells output power and efficiencies of PVPS were analyzed. Water used to cool down the panel was pump outlet flow; thus, no extra power was consumed to decrease PV cells temperature.