If you carry a sealine bag in your bug out bag this video by The pathfinder school will show you how to purify it by boiling a stone in it. This could save a life if your only access to water were a stream or creek in the wilderness.
If you had to drink the water without boiling it your chances for survival would be lessened because you most certainly would end up getting sick from the water.
He also shows how to make a compass from a bag of water. Nice info.
Great for campers,hunters,backpackers and survival situations.
Baja Dry Sack by SealLine