Traveling through Newark, I grabbed a bottle of water after getting off the plane. The counter person (not a trained security agent, mind you), says, "you need to leave the cap here." This got my attention. It turns out that the policy at Newark (not other places I visited recently, just Newark) is that you can't buy a bottled water post-security and keep the cap.

It's a bring your own cap sort of situation I guess. (Are you allowed to bring your own cap?)

I will leave the analysis of the logic to you.