Southeast Wilderness Survival
The human body, much like this planet we call home, is made of roughly 75% water, and therefor water is a prerequisite to maintain life. A healthy, and properly hydrated, body can survive only three days without the intake of water without sustaining severe physical consequences, and will suffer possibly dangerous effects well before that point. Dehydration thickens the blood and inhibits the flow of oxygen to the brain making clear thought difficult at first and later impossible if it's not treated. Re-hydration of the body is a time consuming task, and survival situations are difficult enough when one can think clearly. Water is always high on the list of priorities even in cases where shelter and warmth are an immediate need.
Our planet as a whole has a very large supply of water, but it is not available in all regions. Even in the areas where water is usually plentiful, such as the forests of the S.E. United States, various contaminants will often make it unsafe for human consumption without first being filtered and treated. In a forest environment there are almost always the particles of organic matter; decomposing leaves, and insect larvae. There are also microscopic organisms such a Giardia and E. coli, both of which come from the fecal matter of mammals and can cause some very unpleasant symptoms and can even be very dangerous.