sniper. I would say that is a little expensive. But if you are going to be in an area and need water in an emergency it sure could come in handy.
I have never done it but read where you can run water through a coffee filter, boil it and put a teaspoon +- of bleach in a gallon of water and it will kill all the germs. Always let your wife or girlfriend drink it first to make sure your not going to get sick.
Hell Bear Grills just sticks his face in a mud hole and drinks the water and he ain't dead yet.