Ross, thanks for bringing up pack torque as it relates to carrying of water. High torque is the one problem I have with my Granite Gear Nimubs Ozone, which is very deep in the axis perpendicular my back. I try and load it with dense items near my back and less dense items farther away.
No one has mentioned hanging two 1 liter nalgenes on the front of the pack straps. This reduces pack torque, and of course your water is easily available. (but I don't do that)
Anyway, to answer the thread subject, I carry 500ml soda bottles in each of the side mesh pockets, and if necessary a platypus bladder in the packs hydration pouch.
As an aside, I read plastic bottles designed for carbonated beverages are stronger because of the transportation requirements on pressurized liquids.