Ducklings are, first and foremost, MESSY. Their waterer will become more and more of an issue, I have found if you can figure out how to keep the water mess to a minimum they aren't much harder than baby chicks, they grow like CRAZY as well, which is a bonus.
I have taken rat wire with small square holes, about a quarter inch, and formed it over the top of a baking pan, then sat their waterer in the middle of that. Because they will love love love to take mouthfuls of their food and dabble in their water and sling the whole mess around. It gets nasty and smelly really fast.
Just be ready for them to grow like weeds and to be really messy with their water, and you will have it covered. Good luck!