[rowbow]

I read somewhere to add glycerin to the water in the winter to slow down freezing, has anyone tried this and is it safe? 

[snow white]

Noooooo.   At best it does not work.  At worst it could be harmful to them.  Just change the water 2/3 times a day.  Leave a small stainless steel bowl inside the coop with plain water in.  It will not freeze as much.