The immediate health risk of choking on food or debris that can clog sinus and throat, is one of a few reasons ducks should be expected to be able to at least sponge bath.
I've heard of many first time duck owners of hatchling to adult ducks of all kinds that have had that happen to, as well as had that happen to my first duck while i was gone. some haven't had that trouble yet, but for reasons or luck, but why take the chance..
You could use water ect jugs with holes cut out for their heads to only fit in, for example, as have heard works well, or look up or experiment with other ideas so they can wash heads and not make a mess (hehehe great luck with that!).
Ducks also need to be able to wash whole body and wet oil gland to spread their oils all over them and their ducklings, to stay clean, pest free, dry, and a lot warmer than and at least as warm as chickens as as don't produce as much heat, have to heat those feet and bills.
plus aside from being amusing as all get up to watch, bathing swiming and diving is a natural behavior thats great for bordom and their mental well being. Ducks without water to sponge bath in at least seem to fight a lot more and worse, and ducks without water to bath in don't breed well or at all supposedly, and ducks without enough water tend to get a lot more skiddish it seems. most knowledge or opinions from on here or only from my own scovy only.
Muscovy ducks are known for not needing pool or pond, less cold hardy, and a lot more varied in feed and many habits, are different species of duck more to mostly "wood duck" than mallards or others commonly kept, that are at least mostly mallard breeds.
