Why do we have water towers and what do they do?

Kelly Keegan was showing a visitor the sights of rural Minnesota when her friend asked a strange question: "What are these spaceship-looking things?"

It took a moment for Keegan, a Minneapolis attorney, to realize that he was asking about something that Minnesotans take for granted: water towers.

http://www.startribune.com/why-are-there-so-many-water-towers-in-minnesota-and-what-do-they-do/563803581/