I used to have ducks! I had a kiddies paddling pool from argos. The blue shell ones. They loved it, has a little ramp with 'steps' to get into it.
The only thing I will say that is a downside of keeping them. They left me with not a single blade of grass!

I have ducks too
One thing to remember with ducks is that they can be very messy ,so if you want some ducks for a pretty garden dont forget that they will prob turn half it into mud if they can
if you get ducklings dont give them medicated chick crumbs as the medication is great for chickens but not good for ducks ,also watch what you feed ducklings as if they get too much protien as they are growing they can get angel wing