Coming through security recently at ATH I was told (politely, I admit) by a security person that I couldn't bring my .5 mineral bottle through the check point. I explained that the bottle was empty (I hoped to fill it up at a water faucet after clearing security) and was told that I still couldn't bring it through. I took the cap off the bottle, turned it upside down, and shook it to demonstrate its vacuity, and was told I still couldn't bring it through.

I didn't have time to ask for an explanation of why empty water bottles were prohibited. Can anything here think of one?