Is the water for drinking or for swimming? If it is for drinking, in my coop I have cement blocks around 4 water pails. I use a heat lamp hanging from the ceiling rafters over the pails which keeps them from freezing. You can also buy tank heaters some that lay in the water and some that float. We have some of the tank heaters but with so many buckets the heat lamp was easier. If you have a small pond/pool for swimming out side I wouldn't use a floating tank heater cause they could get tangled in it / burned maybe. I am trying to figue out also how to give my geese and ducks swimming in the winter. I would like to dig a mud pond for them next spring. I hope this helped you.
I beleive in Minnesota you have Fleet and Farm stores. In illinois it's called Farm and Fleet. At any rate they have heated buckets on sale at very reasonable prices here. They would work for ducks. It works for our four. Trouble is the ducks will dirty the water much quicker than other animals so it has to be changed and not added to. We first bought the bucket for a pony. It holds about three gallons.
We use the heated buckets too, but put another bucket inside the heated one to make it easier to clean. Be sure to put a bit of water in the outside heated one so it doesn't burn out. We've used the same buckets for years this way. This is good for drinking water. For bathing water, we do have a pond that stays open most of the year but it does freeze solid in January. We also have a 15 gallon shallow black tub that always has water in it during the day. I used to keep it open with a birdbath heater but now I simply empty it at night and refill it in the morning if the pond is frozen. Even this isn't necessary, but a luxury for my geese. On really bad days, I simply keep them in, under cover, on a bed of shavings with hay. The waterers suffice for those times.