When keeping ducks as pets a pond is recommended as the ducks will be much more happy.
However you can use a plastic kid swimming pool for the ducks to swim in.
The ducks can swim in it and be happy.
My neighbor has ducks and she has a small swimming pool that she installed in the ground as a small pond for them.
She uses a sump pump to drain the water out of it and clean it and then puts fresh water in it.
We live kind of rural and she only has a few ducks as pets.
But she plans to put in a bigger pond in a few years.
You can have a pond dug out if you don't have one.