Ducklings can use chick feeders and waterers until they are several weeks old. They can use a chick waterer until you notice they can't get their entire bill in it anymore. By that time my ducklings were going outside so they just drank out of their pond after that. If you aren't set up for a pond use a 3 gallon black rubber bowl.
It's been awhile since I had ducklings, but I think they used the chick feeder for quite awhile before they had trouble getting their bills into it, so then I switched to a big black rubber bowl.