I have little experience with real winter but it seems to me that if you kept water bottles in an insulated cooler that it would prevent them from freezing or at least contain the spill if any bottles did burst from freezing. Just a thought.
Winters vary greatly, but the short answer is that the water will eventually freeze, it will just take longer in a cooler. By themselves the water may freeze in a few hours or overnight, while in a cooler it could take a few days, but it will freeze eventually.
I also second hat Nate said about the plastic bottles. I used to leave a case of bottled water in the back of the Jeep and they would freeze, and I don't recall any of them actually rupturing.
Of course, there's not a lot of point to having water in the car if it's virtually useless to you when you need it.
Def