Originally Posted by
CATSA SO
Not 100% sure about the exact US regulation, but in Canada (and we're very similar in a lot of cases), you would not be permitted to drink it inside the checkpoint. There are a couple reasons for this. First of all, it slows everybody else down behind you because an SO has to waste time watching you do it and secondly you're technically already in the restricted area.
Wouldn't it take less time for an SO to watch you drink 2 oz. of water than it would escort you out of the restricted area? If so (and I would be surprised otherwise), then that negates reason #1.
As for reason #2, why does it matter if one is in the restricted area in this instance? Isn't it safer to have a passenger drink the nefarious liquid (if the passenger volunteers to do so) as opposed to having the liquid dropped into a container with all of the liquids relinquished by other passengers?