I used the Platypus 6L BigZip waterbag as my in camp water hauler during my section hike last spring and during other summer and fall adventures in the west and in the Smokys. Six liters may seem like a lot, but I drink copious amounts of water and dislike having to make multiple trips to water sources which always seem to be far downhill. I would usually fill up 5 or 5.5 liters and would consume most of this before leaving in the morning. Durability is good. No signs of damage to the waterbag body or on the threads of the spout.

This is a "BigZip" model, which means that there is a threaded spout with cap, along with a large openning at the top, which closes with a mechanism similar to a ziplock bag. During warmer weather the ziplock top works well enough. I hauled 5 L of water up Blood with the bag strapped to the outside of my pack and nothing spilled. However, during cold temperatures the plastic contracts and the zip becomes impossible to close. For those of you starting in the winter or early spring, this may be an issue.

Overall, this piece of gear has served me well. The failure of the ziplock closure during cold weather is an annoyance. The 6L will be staying at home this summer, however, as the capacity is too large when full to fit outside of my pack in a sharp manner. That is, it is hard to hike with it when full and this summer I will have many 20-25 mile waterless stretches. I will instead be bringing 3 2L Platypus regular (not bigzip) waterbags. The weight is 3.2 oz and the cost is $18.