Carbonation decreases the density of a liquid. This can be seen by the fact that carbonated drinks are less dense than non-carbonated drinks. This effect is due to the presence of carbon dioxide gas in the liquid. Carbon dioxide gas is less dense than water, so when it is dissolved in water, the density of the water is decreased.

For example, the density of water is 1.0 g/mL at 25°C, while the density of carbonated water is 0.998 g/mL at the same temperature. So, carbonation decreases the density of water.