"...there are probably even lighter-weight water bottles available,too."
The Aquafina 500ml bottles use ultra thin plastic and are very light. They also squish down to nothing for packing (empty) and can be blown back out to shape with a quick puff. Great for packing a few empty compact bottles for the dry sections.
I also hang an insulated bottle holder from my chest strap so that I don't have to reach behind to get the bottle (shoulder dislocations make that a painful move).
