Abstract: A water valve device includes: a valve unit having an input port for receiving solar heated water from a solar water heating system, a first output port connected to a cold water inlet of a water heating device using non-solar energy, and a second output port; a temperature sensor for sensing temperature of water flowing through the input port of the valve unit to generate a temperature sensing signal corresponding to the temperature; and a controller controlling, based on the temperature sensing signal from the temperature sensor, the valve unit to operate in a first state, where the input port is in fluid communication with the first output port, when the temperature is lower than a predetermined temperature, or in a second state, where the input port is in fluid communication with the second output port, when the temperature is not lower than the predetermined temperature.