Same setup I have. Temperatures in the single digits and I haven’t see any ice. But then I’m in a wooded area which restricts the winter wind considerably.
You are in the teens with “partially freezing”. Can you block it a bit to keep the wind of off it?
Could you take a picture of your waterer and post? I'm a male and having a hard time understanding your description. :)
Is the water still liquid where the chickens drink from?