Disclosed is a water supply system that conditionally fills with heated water. The water supply system has a water tank configured to store and supply heated water, a heater configured to heat water in the water tank, and a sensor configured to sense a temperature of the water in the water tank. In accordance with an embodiment of the disclosure, the water supply system has a water supply unit configured to selectively supply heated water or unheated water to the water tank based on the temperature that has been sensed. In some implementations, this is performed to reduce use of the heated water, which may result in energy savings.