We were told no food or water, unless you had some sort of reason, like if you were diabetic or something. And if you did bring in water, you had to have it in a clear bottle with no label on it. (so you can't hide any notes on/in it).
But during the exams, even brought in water bottles (mostly with labels), and the supervisors didn't seem to notice or care. Our supervisors were so relaxed you could have gone in with a textbook and they probaly wouldn't have said anything.
But for the sake of everyone else, don't go in there with lollies and stuff, cos no one wants to listen to you eating when they're trying to work. If you MUST have gum, chew quietly!