A hot water supply system comprising: a first water heater and a second water heater configured to supply hot water from a hot water storage tank (211, 219) and operate in a mode in which, upon a remaining amount of hot water stored in the hot water storage tank (211, 219) becoming less than a first threshold, power is consumed to generate hot water; and a control device configured to, in a time slot in which the first water heater and the second water heater operate in the mode, control one water heater, among the first water heater and the second water heater, to cause the one water heater to generate hot water prior to a time corresponding to a supply time for supply of hot water by the one water heater in a past time slot, the first water heater and the second water heater operating in the mode in the past time slot, the one water heater being a water heater for which the remaining amount of hot water is smallest, or a water heater for which a difference between the remaining amount of hot water and the first threshold is smallest, or a water heater for which a hot-water amount to be generated is smallest; the system being characterized in that the control device is configured to collect measurement values of power supplied through a power line to a facility in which the first water heater is disposed, and to collect measurement values of power supplied through a power line to a facility in which the second water heater is disposed, and to control the one water heater to cause the one water heater to generate hot water, in the time slot, in a period, prior to the time corresponding to the supply time, corresponding to a period at which an integrated value of a sum of the measurement values collected in the past time slot is smaller than a second threshold. a first water heater and a second water heater configured to supply hot water from a hot water storage tank (211, 219) and operate in a mode in which, upon a remaining amount of hot water stored in the hot water storage tank (211, 219) becoming less than a first threshold, power is consumed to generate hot water; and a control device configured to, in a time slot in which the first water heater and the second water heater operate in the mode, control one water heater, among the first water heater and the second water heater, to cause the one water heater to generate hot water prior to a time corresponding to a supply time for supply of hot water by the one water heater in a past time slot, the first water heater and the second water heater operating in the mode in the past time slot, the one water heater being a water heater for which the remaining amount of hot water is smallest, or a water heater for which a difference between the remaining amount of hot water and the first threshold is smallest, or a water heater for which a hot-water amount to be generated is smallest; the system being characterized in that the control device is configured to collect measurement values of power supplied through a power line to a facility in which the first water heater is disposed, and to collect measurement values of power supplied through a power line to a facility in which the second water heater is disposed, and to control the one water heater to cause the one water heater to generate hot water, in the time slot, in a period, prior to the time corresponding to the supply time, corresponding to a period at which an integrated value of a sum of the measurement values collected in the past time slot is smaller than a second threshold. to collect measurement values of power supplied through a power line to a facility in which the first water heater is disposed, and to collect measurement values of power supplied through a power line to a facility in which the second water heater is disposed, and to control the one water heater to cause the one water heater to generate hot water, in the time slot, in a period, prior to the time corresponding to the supply time, corresponding to a period at which an integrated value of a sum of the measurement values collected in the past time slot is smaller than a second threshold.