We live high in the Rocky Mountains, and have to deal with both frozen water and frozen eggs for most of the winter months. Because fire is such a major concern for us we're not comfortable with electric heaters! Instead, I picked up two metal water fonts (I had to dig a while to find them, but I think they came from tractor supply or some other big chain). They have been much sturdier than plastic, and are less susceptible to temperature shock than glass.
We check on the birds twice a day, morning to release them into the yard, and evening to close them up. When it's bitter out we fill the font 3/4 full with the hottest water the utility sink makes (which is scalding!) and hang it out, then bring in the previous (often frozen) font and give it a short hot bath to start the melting. Usually in 12-ish hours when its time to switch again the ice is melted enough to dump and refill. In the coldest temps it freezes over, but not until about the time to switch. (I often check for eggs midday to catch any that are starting to freeze)