All vessels contain air when seemingly empty.
Do all liquids contain air?
Yes; all liquids contain air.
Where is the air in a liquid?
The air is among the particles which compose the liquid.
Is there air in water?
Yes; there is air in water.
Of what use is the air in the water?
It is used by the fish and other creatures that live in the water.
How do the fish and other creatures use it?