Carbon dioxide is an acid and the product of carbon dioxide reacting with water. Carbonic acid plays an important role in the acid-base balance, both when it comes to the water as well as the blood and body fluids.
Function & Details
That familiar sparkling triggered by CO² also makes for good circulation in the oral mucosa, thus stimulating saliva production. The sparkling also makes the stomach feel full, which is why athletes, for example, prefer water which is not or only slightly carbonated.
The carbon dioxide also has an antibacterial effect, thus keeping the product, i.e. the water, fresh for longer.