For me the main advantage of shop-bought bottled water is that it's stamped with an expiry date, which is usually a couple of years from the purchase date. I'm not really comfortable with the "stick some bleach in it and it'll be OK for 6 months" approach. Of course, the expiry date is only valid if the bottle is sealed, so I don't attempt to transfer it to any other kind of container for storage.

I buy 0.5l bottles which I find convenient for camping, and 4-packs of 2l bottles which are the cheapest I can find locally. I don't attempt to keep more than a few weeks drinking supply.