Another Wisconinitte here with the same question.
What I wonder about since this is our first year with ducks is the mess they make with their water bowl. I'm afraid they will have an ice skating rink in their coop and run.
Btw we are going to be building a new coop just for the ducks, what do you reccommend?? We have about 13 Runners, 2 mallard drakes, and a pair of Roens.
And as long as I'm at it I may as well ask you what you are feeding your ducks?  And how often would  you need to feed in winter??
Sorry if I hijacked this post. I just thought others in the colder climates might have these questions as well. I'll edit and delete my post if you feel I should. (Just PM me and I will)
Anxious to here others opinions on the water issue for ducks in winter. I was under the assumption that they need water 24/7 and have to have it while they eat. I actually put their food in water since I feed a semi mash mix.
I did see a guys duck coop that actually had a pond built right in it. All he did was dug an area that he wanted for the pond, buried pvc drain pipe with a pip burried I don't know how many feet away from the coop.  It was made of poured concrete. Nothing fancy but the ducks sure loved it. He had a drain plug so when the pond got dirty he just pulled the plug and could rinse the pond with a hose and it all drained out away from the coop. Of course it would have to be buried deep enought not to freeze in our colder climate.  He has a pole barn with all sectioned off coops for his chickens with individual runs on the outside. He says it really doesn't get that cold in the building but I don't know if the pond freezes or not. The pond was inside. Not real big but served the purpose. 
Must be nice to be able to build a whole pole barn just for your chickens, or should I say have one built which is what he did. My poor horses are still waiting for a pole barn !!! LOL