A water heater control system comprising: a commercial power supply; a photovoltaic power generator interconnected with the commercial power supply; an electrical load circuit including a storage-type electric water heater configured to use power from the commercial power supply and power generated by the photovoltaic power generator to perform a water heating operation of heating low temperature water to high temperature water and storing the high temperature water; and a control device configured to control the water heating operation of the storage-type electric water heater based on purchased power fee data for purchased power supplied to the electrical load circuit from the commercial power supply, wherein when controlling the water heating operation of the storage-type electric water heater, there is a water heating-limiting operation mode and a water-heating continuing operation mode, the water heating-limiting operation mode being a mode in which the control device calculates or acquires, at prescribed time intervals, said purchased-power fee data and when the purchased-power fee data exceeds a standard monetary amount, suppresses or stops the water heating operation of the storage-type electric water heater to limit the water heating operation, the water-heating continuing operation mode being a mode in which the control device continues the water heating operation of the storage-type electric water heater regardless of whether the purchased-power fee data exceeds the standard monetary amount, the control device switching between the water heating-limiting operation mode and the water-heating continuing operation mode based on a time slot. a commercial power supply; a photovoltaic power generator interconnected with the commercial power supply; an electrical load circuit including a storage-type electric water heater configured to use power from the commercial power supply and power generated by the photovoltaic power generator to perform a water heating operation of heating low temperature water to high temperature water and storing the high temperature water; and a control device configured to control the water heating operation of the storage-type electric water heater based on purchased power fee data for purchased power supplied to the electrical load circuit from the commercial power supply, wherein when controlling the water heating operation of the storage-type electric water heater, there is a water heating-limiting operation mode and a water-heating continuing operation mode, the water heating-limiting operation mode being a mode in which the control device calculates or acquires, at prescribed time intervals, said purchased-power fee data and when the purchased-power fee data exceeds a standard monetary amount, suppresses or stops the water heating operation of the storage-type electric water heater to limit the water heating operation, the water-heating continuing operation mode being a mode in which the control device continues the water heating operation of the storage-type electric water heater regardless of whether the purchased-power fee data exceeds the standard monetary amount, the control device switching between the water heating-limiting operation mode and the water-heating continuing operation mode based on a time slot.