You want to make sure they have an obvious way in and out of it. I laid out a pile of creek stone, gradual steps, and set a cinder block inside for the exit. They walked round and round it for awhile, knowing it was water, knowing they wanted in it, but not knowing how the steps worked.
How old are yours? Mine were 4 weeks when I introduced them to the world of baby pools. I didn't use food, I just gave them time, and locked them out of the coop!
For indoors, you can build a catch system for all that water waste. A wooden frame made to fit around a flat plastic tote, with rabbit wire on the top. Set the waterer in the middle, and it catches all the waste water, preserving the bedding. I have about 8-10 inches of wire around the waterer, which seems to be enough. I bought a larger 3 gallon waterer, and my frame isn't big enough to be effective, with only 3-4 inches around. So take the size of the waterer, added a perimeter of 8+ inches, and that's the size of tote/frame you need.
My next duck house will be up off the ground, with a section of rabbit wire floor, that I can slide a concrete mixing pan under from outside. Then I can pull and dump it a lot easier and they don't have to climb on anything to get to water. But I had to work with what I had. The next duck house though, will have characteristics of both a rabbit hutch and a chicken coop.