You have to be so careful with ducklings and water. They LOVE water the most and struggle to make good decisions.
My rules for duckings and water.
Week one only drinking water from a drown-proof waterer.
Week two they are allowed a shallow bowl full of water. They must be able to get in and out of the bowl without help. Water should be warm and they need to be dried or have a warm place to dry off. Never left unsupervised in the pool and if they get too wet they need to be done.
Once they are taller, week three, they can have a bigger pool. Again they need to be able to get in out on their own and a warm place to get dry. Supervision is still a good idea.
Week four they can have as much pool time as they want.
These are my rules for when we have lots of ducklings. If I only have a few it is easier to let them have more water in a bathtub or a sink.