My husband teases me when he hears my baby ducks as soon as they see me they quack quack quack and he goes agua agua agua LOL. I have a gallon chicken waterer i can get it to last a day with 2 ducklings. I have a broiler pan under it so the pan collects the spilled water. It helps keep the bedding dryer than if the pan was not there. Those ducklings love their water LOL
Since they are waterfowl - it is a whole new game with ducks. Please remember that first part - they are waterfowl.
Here are some good ideas on water management. They need water. They need water that they can dunk their heads into many times each day or they risk serious eye, sinus, ear, respiratory infection.