i.e. Nalgene bottles? I'm one of those eco-friendly weirdos who can't justify buying bottles of water - if we can't bring in reusable bottles, we'll buy bottled water for our fridge, but I'd rather bring in our own.
Yep! We've done this many times. If it's a hot time of year, we'll even put extra bladders in the CamelBak . When the kids were younger, it'd keep them drinking because the pack got lighter as they emptied the water