This article (http://www.youtube.com/?v=FPH5vd__uJQ&) summarizes the importance of a survival water filter. Your main concern during a disaster is having clean water, because having access to clean, potable water is usually the first basic element that you will not be able to get when faced with a crisis situation. You will need approximately a half a gallon of clean water for basic survival, or more if you are in a stressful situation that causes you to use more water. This does not include water you will need for hygiene and basic cleaning, like washing your dishes and hands.
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