In terms of bouncability, I agree with your concerns about durability. That's why I said maybe double bag it and certainly store it in a rigid container. But every winter I always miss a water bottle when I'm prepping my car for the cold. ANd every spring I have a wet spot someplace that needs to be taken care off before it turns into a moldy spot, and a bottle that burst from the freezing. You'll note that I proposed freezing ice, with room to spare, so that wouldn't happen.

As for reusing, I wasn't thinking so much about resealing it although I don't see why you couldn't. I was thinking it can be used to cook in, ala freezer bag, or for general storage.

As for the purity... I worked in a bottling plant for a while just after high school. I saw some scary stuff. If I was to boil water, laddle it, still boiling, into a mold which then goes immediately into the deep freeze, it will be AT LEAST as clean as what you buy on the shelf.