Overnight when they are sleeping they do not need water. If you do not leave them locked in there for long periods of time when they are awake, you do not need water in the coop.
Ducks are messy with water. It’s just the way they drink.
I don’t use the “normal water can”, whatever that is. If it’s what I think it is, put it in a corner up on a block or something so they don’t scratch as much stuff in it to get it dirty. Put it in a corner or against a fence, post, or some type of support and rig up a bungee cord with a hook or snap lock so you can keep it upright. You might need to put a block or something between the support and the can where you put the bungee cord so they can’t tilt it toward the fence, wall, post, whatever your support is.