Duck pool in sub-freezing temperatures

[AKnewbie]

Is it doing them more harm than good to be providing them with a wading pool in sub-freezing temperatures?
I have 2 ducks and it's 15F right now. They have a 5 gallon rubber container that I am planning on using as a wading pool for them so they can get their pool fix.Obviously it gets taken out sometime during the day and will be refilled again the next day.
I am concerned about them getting wet in those temperatures though. Will I be doing them more harm than good by allowing them to swim in it at least in the morning?

 

[CelticOaksFarm]

we arent in a cold climate but from reading those that are many give a small pan of warm water every few days to bath during coldest days. Otherwise a bucket is used for drinking water.