Get a syringe. Fill it about a quarter way with water. Turn it facing up and squirt out any air bubbles. Block the end where the needle goes with your finger. P

Get a syringe. Fill it about a quarter way with water. Turn it facing up and squirt out any air bubbles. Block the end where the needle goes with your finger. Pull the plunger back hard as if you're filling it all the way up. You'll pull a hard vacuum and you'll see the water inside bubble as it boils at room temp.