I've heard about people using water cooler bottles for storage, and I would assume that they're just as good as individual water bottles. Since they're clear, I'd keep them out of the light just to make sure nothing grows inside of the bottles.

I worry about the tear band lids, but if the system works to keep them from breaking open in shipping it must be pretty solid.

Stacking them might be a problem unless you put them on their side and stack them in a pyramid with chocks in between the lowest bottles to keep them from rolling. You might also be able to put a piece of plywood over a level of bottles with more bottles on top of that.

If you're going to buy the water bottles empty, I'd buy the kind with screw on lids and handles just to make them easier to move. Before that, I'd go to Amazon and get their 5 Gallon stackable carriers. Depending on how much you plan to store, you may even want to buy a 55 gallon water barrel. I've seen kits for as little as $60 that include a 55 gallon drum and siphon pump. Others have obtained used barrels for a lot less.

It costs my neighbor about $8.50 per 5 gallon bottle for Deer Park IIRC, but they have to get 3 at a time and the delivery man collects the empty bottles.

In any case it's better than nothing.