As P_L wrote, I am not sure there is an answer to the tap water question. Too many variables. I have the same problem with the climate (MidWest USA), now exacerbated with my recent infatuation with a Camelbak essentials pack. My solution for this winter is probably going to be a dry reservoir and two Lexan Nalgene bottles, coupled with lugging the darn thing in and out of my personal vehicle each day.

My carry water doesn't have a chance to get more than about 2 weeks old year-around so storage life of that is not an issue - it's just the freezing. My take on the question is that if it was good to drink when you put it in a clean container and it does not have visible gunk in it, it's OK to drink <gasp> - well, that works for me, anyway. Worst case I have a least a bandana and iodine tabs with me.

Long term storage of bulk water is a whole topic on its own. I have some good 5 year old tap water (about 330 gallons) back in the store room... and what P_L wrote is sound reasoning IMHO. But my bulk water has been in a dark constant cool temp place all that time. It's a little flat to my taste, but not as flat as boiled water. I should cycle it... I think I wrote that last year... but it's still good (eyedropper samples sipped annually).

Tom