Regardless of the season, the temperature of Su'ao Cold Springs remains a constant 22 degrees Celsius year round meaning that the water source lies underground at a certain depth, isolated from the weather and surface water. With the exception of winter when the water temperature might be higher than air temperature, the water is always cooler hence the name "cold springs". There is abundant underground water in the downstream of Su'ao River. When carbonated water bubbles to the surface from thick layers of limestone, its temperature stays near 50 degrees Celsius. However, the water is mixed with colder underground water on the top layers during the ascension while carbon dioxide in the water also removes the heat in the water to further lower its temperature. The end temperature of the water when it reaches the surface is 22 degrees Celsius and the carbon dioxide in the water rushes out to create bubbles.
During the Japanese colonial era, Japanese merchants saw a business opportunity in carbonated cold springs. They consequently established the first soda factory in Taiwan at the foot of Qixingshan. The product was a cold spring soda named Namunei made by taking the carbonated cold spring water, reducing the carbonic acid gas, and adding sugar and flavors. The soda was bottled in the traditional soda bottles sealed with marbles, the first of their kind in Taiwan. To drink it, one needs to tear off the seal and push hard down on the opening to make the marble drop into the bottle with a pop sound and the soda come out. The excitement of popping the marble and the sharp taste when the soda first hits the back of the throat made the marble soda a huge hit and a favorite childhood memory for many.
