A great way to keep water from freezing is by digging a hole below the frost line, putting your water containers in it, covering them with a large piece of plastic (or by putting them in a large plastic bag) and then filling in the hole with a thick layer of straw. You can even mound the straw over it to provide more protection.
You can also get the average ground temperature plus the average ambient temperature then calculate how much straw you will need (everything has an R-value) to keep it all insulated.
Ohh, nice tips, @jacobpeacock ! I have a medieval quarter home here in Italy, where my cantinas (cellars) are below the ground, built directly into the rocks of the steep hillside, and they give incredible geothermal regulation of heat winter and summer. Maintains a relatively stable temp. :-) Amazing natural architecture, back from when we hadn't separated mind body and spirit!
That cellar (cantina) setup sounds pretty cool! Especially since it is in stone!