It would have to be awful cold for an awful long time for a water tower to freeze solid. The water is typically moving most of the time as it flows in and out. Water being pumped into the tower is going to be above freezing. And the large mass of water makes it pretty hard to get that cold. In colder climates, they may even have some sort of heating device, it only has to keep the water above freezing. And I'm sure the top edges get some freezing around them. ASS yes it could, anything could happen!!!