I would not be comfortable, personally, with keeping them overnight without water. Ducks drink often and they drink a lot. I have seen my muscovies up at night drinking many times. I'm not saying it's going to kill them--I just don't think its the kind thing to do. (Ducks always seem more relaxed and content to me with water accessible nearby too, probably for instinctive reasons.)
I keep mine in an open pen on dirt, with a deep bedding of leaves and/or wood chips. THey can't get things that muddy unless they are on bare dirt! If these get wet it doesn't much matter. The top is covered with netting so they can't fly or climb out when it's closed, but they sleep usually in a three-sided shelter attached to that run area. As long as there is enough bedding, and it gets stirred occasionally with a rake, it's fine--it's almost never completely dry, and clean is a relative term, but even with rain and splashing and lots of pooing, it normally doesn't stink and isn't what I would call unhygenic (and our standards are fairly high--I take livestock welfare pretty seriously, plus we have guests visiting often and my brother lives just downwind of the pen too). Sometime we put their larger water tub out on the grass near the pen when it's open, and move it around periodically so it doesn't kill the grass. But as a rule we always make sure they have access to at least a small portable jug waterer during the night if nothing else.
My arrangement is not predator proof however, as we have no predators here to worry about.
