Well, splashing water all around and making a mess is how geese bathe themselves and keep clean, so it seems counterintuitive to prevent them from doing it. Especially in winter, when pristine plumage is paramount to keeping them warm and dry.
cut a hole near the top of a 6 gal. bucket. just enough for them to get their head in and can still splash a little water to preen themselves. i dump out the frozen in the morning and give them hot water. i don't put water inside the coop. they only get their pool from may to nov. too cold to maintain up here in winter.