Water pipes will burst, water mains will freeze solid and water ponds in your back yard are subject to harsh freezing.

Do you have fish or frogs in your ponds? Make sure the water doesn’t freeze all the way to the bottom.  Fish and water life will survive by assuming the temerature of the water unless of course the water is frozen. Then they become fishcicles. 

If you have the ability to cover the pond in very cold weather, it will insulate the air underneath and keep the water at slightly a higher temperature. Also your spigots outside are subject to breaking in severe weather. Places such as your local hardware stores and home centers sell covers for those outside spigots. For a couple dollars and 5 minutes of energy you could save a 200 dollar plumbing bill.  Sounds like a deal to me !