I have read that baby ducks should not go into the water until they have all of their feathers and have the water repellent oil on their skin. the babies get the oil from their mom's feathers so water won't get on them. So how do you dry your baby ducks after they go for a swim? don't they get chills and die?
Since I brood them indoors, I give them warm water baths in the bathtub. I towel them dry and move them to their warm brooder. They will still be damp, but they dry quickly and it is a good way to get the little mudlings clean after they have been outside playing with the dirt around their water...
Last year I would let the ducklings in a shallow pan of water on hot days outside for no more than 5 minutes. I never had to towel them dry, they weren't in it long enough to get soaked, they always appeared to be fluffy.