A heat pump water cooling and heating system comprising: a first heat source unit including a water heat exchanger and an air heat exchanger; a second heat source unit including a water heat exchanger and an air heat exchanger; and a control unit (17, 27) configured to switch a heating operation in which the air heat exchanger (16, 26) serves as an evaporator and a defrosting operation in which the air heat exchanger (16, 26) serves as a condenser, characterized by further comprising: a joining point where cold or hot water flowing out of the water heat exchanger of the first heat source unit and cold or hot water flowing out of the water heat exchanger of the second heat source unit join, wherein, in a case where one heat source unit (11, 21) of the first heat source unit and the second heat source unit performs the heating operation and an other heat source unit (11, 21) of the first heat source unit and the second heat source unit performs the defrosting operation, the control unit (17, 27) is configured to stop the defrosting operation of the other heat source unit (11, 21) and reduce a volume of water flowing out of the water heat exchanger of the other heat source unit to the joining point when the heating operation of the one heat source unit (11, 21) becomes inexecutable. a first heat source unit including a water heat exchanger and an air heat exchanger; a second heat source unit including a water heat exchanger and an air heat exchanger; and a control unit (17, 27) configured to switch a heating operation in which the air heat exchanger (16, 26) serves as an evaporator and a defrosting operation in which the air heat exchanger (16, 26) serves as a condenser, characterized by further comprising: a joining point where cold or hot water flowing out of the water heat exchanger of the first heat source unit and cold or hot water flowing out of the water heat exchanger of the second heat source unit join, wherein, in a case where one heat source unit (11, 21) of the first heat source unit and the second heat source unit performs the heating operation and an other heat source unit (11, 21) of the first heat source unit and the second heat source unit performs the defrosting operation, the control unit (17, 27) is configured to stop the defrosting operation of the other heat source unit (11, 21) and reduce a volume of water flowing out of the water heat exchanger of the other heat source unit to the joining point when the heating operation of the one heat source unit (11, 21) becomes inexecutable. a joining point where cold or hot water flowing out of the water heat exchanger of the first heat source unit and cold or hot water flowing out of the water heat exchanger of the second heat source unit join, wherein, in a case where one heat source unit (11, 21) of the first heat source unit and the second heat source unit performs the heating operation and an other heat source unit (11, 21) of the first heat source unit and the second heat source unit performs the defrosting operation, the control unit (17, 27) is configured to stop the defrosting operation of the other heat source unit (11, 21) and reduce a volume of water flowing out of the water heat exchanger of the other heat source unit to the joining point when the heating operation of the one heat source unit (11, 21) becomes inexecutable.