I'm in northeastern Missouri so no stranger to really cold winter weather. It can get in the minus teens here in January/February.
Tried the heated dog bowls. They work but seldom last more than one or two seasons for me before they conk out on me.
Last year I went to home made heaters that consist of a metal cookie tins with a coffee cup heater inside. Luckily I have power to my coop so no problem and the heaters work great. I have old metal mixing bowls that I set on them and no more frozen water.
A member here on BYC, passed on the idea to me. You can find the easy instructions here:
https://the-chicken-chick.com/make-cookie-tin-waterer-heater-under-10/