Recently, since water heat energy was included in renewable energy in Korea, interest in water source heat pumps for space cooling and heating has increased. Since the temperature of the water is lower than the ambient temperature in summer and higher in winter, a water source heat pump has an advantage in COP over an air source system. However, when the water temperature drops in winter, the operation of a water source heat pump becomes limited due to the risk of freezing in heat exchangers. In this study, we analyse the heating operation characteristics according to the change in the temperature of the water and propose operation modes to overcome the drawbacks in heating operation. A test loop of 20 kWth was constructed. As operation modes for utilizing low-temperature water sources, reverse cycle operation, heat storage tank-associated operation, and heat source compensation operation were derived. Among them, test results and operation characteristics analysis for heat source compensation operation are presented. These results tested in the laboratory can be used to design the optimal operation modes for water source heat pumps when applied to actual buildings in the future.