We thought seriously about buying a heated hose, and we spoke with several people locally who had experienced good success with one model in particular. Ultimately we did not because the run from the house to the duckhouse is more than 100', and you can't daisy chain the heated hoses.
For what it's worth, our current routine with this bitter cold (-5 to -10 F for the foreseeable future) is to carry out a small pail (full) and a large pale (empty) in the morning. We also bring out their "soup" and put it in the run. I top off the heated water bucket in the run, and we then open the duckhouse door. Because they don't have access to water overnight, we let them all get a good drink. Then I empty the heated bucket in the run into the large empty bucket I brought out. I dump that, and then go fill it in the house. Finally I fill the heated bucket with fresh water, and we're done...except for a mealworm snack, of course.