Ducklings can most definitely drown, because they are not yet waterproof. However, they will float for a long time before they drown. But without an easy (and I mean EASY because they are not usually gifted with strong problem-solving skills) exit and, better yet, an attentive mama, they will stay in past the point of waterlog. Most people don't recommend swimming-depth water for ducklings until they are fully feathered except under direct supervision (this is what you're usually seeing in pictures of bath tub ducklings). In the wild, the mother duck carefully regulates swim time, and ensures the ducklings can get out safely. And anyway, the wild is hardly a good model if you want to raise most of your babies as wild ducklings have a survival percentage somewhere in the low teens. So the best bet is a waterer like those already suggested. I just wanted to be clear that giving them *more* water is not necessarily better. This is definitely a case of "just enough is perfect."