I leave water in my car in the UK and whilst we don't get temperatures of silly below, we often get -5 to -10 (or worse in the hills). I've noticed that the water rarley freezes completely. Since the ice forms at the top of the container first I simply store them upside down (they are leak proof!). That way the ice really forms at the bottom of the container and the top/spout is clear. Simple but effective.