"This is a water system similar
to a camelback, a water bladder inside a nylon bag with a drinkig tube. You can put the bag in or ontop of your pack and drink without
messing with a bottle. Mine
holds 100 oz of water. The best part is an adapter that
allows you to attach your
waterfilter to the tube and pump directly into the bag.
this acapter can be installed to any waterbladder system and simplifies refilling those plastic bags. Very good idea."