This is what you do. Water bottle technique basically. Get the water that comes in a large pack from a wal-mart/Safeway (the smaller ones that are made of that thinner plastic) cause they have shittier lids. Simply dip the caps into boiling water at home. That should soften the plastic and make it easier to take off without busting the seal. The cap should be fairly easy to put back on even after it cools down.
Also. I like to throw several normal waters around it in my bag when going through security
Do you ever have a problem with them opening any of them?
I think I read that they weren't letting 'factory sealed' bottles in?