While we've no way of knowing what actually happened or who instituted this or why, I would note that there have been several instances of suspect things along the Mississippi River--and many cities along it seem to have cells. I suspect that some cells use it to move people and materials. (I realize that Columbus is at least a hundred miles east of the river, but this seemed like a good place to mention it.)
While the phone call could have come from a run-of-the-mill prankster, I wonder if someone was assessing the response? Gathering a bunch of citizens in one place to pick up water is helpful if someone is looking for a crowd...
OTOH, if you can't penetrate a municipal water supply, you might opt for creating a scare in order to pass out poisoned water before the authentic supplies arrived--as long as you knew what authorities and and citizens were expecting.