Funny, I was just thinking about this earlier in the day. I do not have power to my coop and cannot (code), so I will be hauling water. I'm resigned to that, but it doesn't stop me from wondering if there is another way.
Fred's Hens is right. Something like salt, while able to lower the freezing temperature of water, is not good for chickens. While it's conceivable that some vitamins could manage the trick just as well, there would have to be what is likely a lethal dose dissolved in the water to avoid freezing. Another choice would be alcohol, but I don't want drunk, cold chickens (plus, again, the amounts required would be high). Antifreeze is toxic, so that's a no-no too.
I'll be thinking about this over the winter, no doubt.