When using a can of compressed air, the liquid residue left behind is water and it comes from air...as in what's in the atmosphere, not what's in the can.
The can's contents are rarely breathable air (which is actually mostly nitrogen).
The compressed gas inside the can is actually a liquid because it's compressed at high pressure. It's *NOT* water. Water is a liquid at room temperature and can't be compressed. The compressed gas then has a very low boiling point meaning that it vaporizes at room temperature. More to the point, if the compressed gas were not compressed it wouldn't shoot out the can when released.
In other news, as a compressed gas is released into the atmosphere it expands since atmospheric pressure is way lower than the pressure inside the can and as soon as the compressed gas hits the atmosphere it boils. Now as a compressed gas expands it cools down and as compressed gas cools down it can condense any gaseous substance suspended in the air (like water molecules) into liquid water or into solid ice depending on such variables as relative humidity as there must be adequate gaseous water molecules to condense, the type of compressed gas, and naturally the temperature differential caused by the release of the compressed gas.
That's why it's possible to take a can of compressed air, shake it vigorously, turn it upside down and freeze stuff with the escaping gas.
It's worth noting that there's a serious danger of frostbite and property damage if doing this.