A low tech way of keeping
water from freezing for livestock is to boil a lot of salt into water
bottles and place those bottles at the bottom of a container.
Pour water over top of the bottles keeping them submerged.
My Mom tried this recently
and reports it works at very low temperatures.
Hmmm... Intriguing idea. What is the maximum and minimum size of the container that you are putting the bottles? I mean, if you have one bottle, is there a minimum or maximum size that the one bottle can handle before the larger container becomes too much?
I wonder if you could put antifreeze in bottles and do that as well? Sounds like an experiment is in order!