Plastic paddling pool. Your ducks will love splashing and swimming in this paddling pool.
Tried and tested by us on our duck farm - very hardwearing (ours have survived hard frosts, horses stepping on them, pigs wallowing in them, etc.)
It is a common myth that ducks need a pond, they do not. A pool like this is ideal as it can be easily cleaned and water changed. It is important that ducks have access to water to clean their face and bill, a drinker is not sufficient.