I have a purchased gallon of bottled water in the car. I save plenty of $$ just drinking from it in my travel mug vs buying dunkin donuts coffee all the time. Also I treat it just like my gas tank, when it is 1/2 empty I get a full one from the basement, drain the 1/2 empty making juice from concentrate for my breakfast and wash and refill the gallon from the tap and put it in the basement for the next time. In the basement I have some 20 or so of these gallon jugs mostly unopened. unopened ones are presumed good for 5 years. Opened ones are cycled through the car and camping activities as described above. I don't worry about the storage life of the opened ones since they are cycled in months if not days depending upon usage.

I forgot to add what I do in winter - I bring it in the house just like I do my lunch box. In the morning it goes to the car and in the evening it comes in. I have never had it freeze up solid during single day 8 - 10 hours in the car even in winter in NH with -20 F occasionally. It is never less than 1/2 gallon of water so it freezes somewhat slowly and the car is usually warm when I park after the hour commute to work.