Why don't water towers freeze solid in the winter?

Wisconsin water towers: Their stories and what they do, besides

Why do freezing pipes burst?

Ice road - Wikipedia

Wisconsin water towers: Their stories and what they do, besides

We all know what temperature water freezes at, right?!

lessons « Galaxy Dreams

Why Does Water Freeze from the Top Down?

Structural Engineering, HowStuffWorks

Frozen stream of water coming out of leaking water tower. Near