Your comment re: water bottles made me want to look this up. Apparently, it's quite easy to reseal a bottle. https://www.youtube.com/watch?v=abosduPhns4 https:

Your comment re: water bottles made me want to look this up. Apparently, it's quite easy to reseal a bottle. https://www.youtube.com/watch?v=abosduPhns4 https://www.youtube.com/watch?v=abosduPhns4 So, I suppose if TSA let people bring in a bottle of "water" from a store just outside, this could easily be faked where you bring in a couple of bottles of bleach and ammonia (although, I don't know how those chemicals would do with the plastic from some water bottles). It kind of makes sense to take a hard-line on water bottles, even if they're sealed, even if it matches the kind of water they're selling just behind you at the airport, and even if you have a receipt, because all of those things are trivial to surmount.