A hot water storage system comprising a heat pump hot water dispenser and a hot water tank for storing water that exchanges heat with refrigerant at a refrigerant-water heat exchanger, wherein the hot water storage system heats water stored in the hot water tank or water fed via a water inflow pipe by the hot water dispenser and feeds the water into the hot water tank, the heat pump hot water dispenser comprising: a heat pump cycle device connecting at least a compressor, the refrigerant-water heat exchanger, a pressure reducing device, and an evaporator by pipes, the refrigerant-water heat exchanger being configured to allow refrigerant and water to exchange heat; a flow rate detection unit for detecting a flow rate of water flowing through the refrigerant-water heat exchanger; and a control unit for controlling operation of the heat pump cycle device, the control unit having, as operation modes of the heat pump cycle device, a circulation mode for circulating water between the hot water tank and the refrigerant-water heat exchanger, and a hot water storage mode for storing water in the hot water tank, wherein the hot water storage mode differs from the circulation mode in that water supplied via the water inflow pipe is heated by the hot water dispenser and stored in the hot water tank, and water is not fed to the hot water dispenser from the hot water tank, the control unit being configured to determine an occurrence of abnormal water supply disruption and suspend the operation of the heat pump cycle device when a flow rate of water detected by the flow rate detection unit continues to be lower than a threshold for a set time period or longer, the control unit being configured to switch the circulation mode to the hot water storage mode after the control unit determines the occurrence of abnormal water supply disruption while the heat pump cycle device is operating in the circulation mode. a heat pump cycle device connecting at least a compressor, the refrigerant-water heat exchanger, a pressure reducing device, and an evaporator by pipes, the refrigerant-water heat exchanger being configured to allow refrigerant and water to exchange heat; a flow rate detection unit for detecting a flow rate of water flowing through the refrigerant-water heat exchanger; and a control unit for controlling operation of the heat pump cycle device, the control unit having, as operation modes of the heat pump cycle device, a circulation mode for circulating water between the hot water tank and the refrigerant-water heat exchanger, and a hot water storage mode for storing water in the hot water tank, wherein the hot water storage mode differs from the circulation mode in that water supplied via the water inflow pipe is heated by the hot water dispenser and stored in the hot water tank, and water is not fed to the hot water dispenser from the hot water tank, the control unit being configured to determine an occurrence of abnormal water supply disruption and suspend the operation of the heat pump cycle device when a flow rate of water detected by the flow rate detection unit continues to be lower than a threshold for a set time period or longer, the control unit being configured to switch the circulation mode to the hot water storage mode after the control unit determines the occurrence of abnormal water supply disruption while the heat pump cycle device is operating in the circulation mode.