I don't think it's "used" per se. You know - likely still in the container. But the most obvious reason would be that it might be easier to not take them if not checking in luggage.
As far as water goes, once we dropped off our rental car, but I went to return the car but left the rest of our party at the terminal. There was a skycap and I asked if they wanted the water, and they gladly took it an placed it in a cabinet there. But that depends on the transportation options.