I've often wondered about storing water in one's car when it's below freezing. I usually take out the water bottles for a couple of months each winter (unless heading out for an extended trip in the mountains) due to concerns that they will eventually burst/crack with the temperature extremes, but I really really don't like the idea of being without some extra water, even in town. A couple winters ago temps dipped below -19F/-28C for a few days; and it can get colder than that some years.