This is a great hands-on experiment to show kids. Make sure to wear safety glasses, as the pressure inside the bottle makes the cap fly very far. Also do not point the bottle at anyone.
This experiment will show you how to make steam come out of a water bottle without heating it. A simple and fun and easy pressure experiment is awesome.
When you squeeze the bottle, the pressure increases. This causes the temperature inside the bottle to rise. When you release the bottle, the pressure decreases. This causes the temperature inside the bottle to fall and the water molecules to condense.
Start off with just a small amount in the water bottle as seen here. Actually you do not need any water in the bottle as it should still work. Make sure the cap is not on to tight as you will not be able to twist the bottle. Its takes practice to get the cap on just right, but not to tight. You are going to twist until you can not twist anymore.
Point the cap of the bottle away from you and quickly release the cover. If you twist the cap too slow then the steam will not rise from the bottle. You need all the pressure to be released at once, not over time. When you twist off the cap correctly, it will shoot out. This is why you point it away from you and others. This is also a good reason to wear glasses. The best way to twist the cap off quickly enough is to hold the bottle itself with one hand, then your other hand, hold the top of the bottle. Use your thumb to apply pressure to the start of where the cap can twist. When you use enough force the cap will pop off.
After the cap pops off, hold the bottle upright and slowly squeeze the top section. This should start to make the steam slowly pour out.