Q: How much water is on Earth? A: There are over 300 million trillion gallons of water on earth. If we divided it evenly, each person would have 40 billion gallons to themselves.

Getting lost or stranded in the wild is something that could happen to just about anyone. Day hikers, tourists, Sunday drivers and experienced outdoorsmen are all subject to circumstances beyond their control. Any and all of them could end up alone and lost, with only their wits to rely on for survival. The single most important thing you need to live is water. If you're resourceful and know where to look, you can find or collect good drinking water in just about any environment on Earth.

­To maintain good health, the human body needs a minimum of two quarts of water per day [source: Field Manual 21-76-­1]. If you're lost in the wild, chances are you'll be exerting yourself, and you may be in a hot or cold environment. Both of these factors mean you should drink more than the minimum amount. It's easy to think that a cold environment might pose less of a risk, but that's not the case. You may perspire less, but you lose water through your skin because of the dry air. You should also drink more water if you're in heavy winds.

Your body is about two-thirds water and uses it to help circulate blood, process food and assist other internal processes. If you use more water than you take in, you'll begin to suffer from dehydration. With severe dehydration, your cells shrink and circulation stops, causing a lack of oxygen flow to your muscles. Dehydration can start as soon as six hours of not having water, and more than a full day without water is cause for serious concern. The human body can only live about three days without it.

Video Gallery: Water, Water Everywhere There are over 300 million trillion gallons of water on earth -- if we divided it evenly, each person would have 40 billion gallons to themselves. To learn more about water and it­s amazing properties, check out this original HowStuffWorks video.­

Now that we understand the importance of water, it should be pretty clear that your shelter should be as close to a water source as possible. If you're lucky enough to find a source, you need to make sure you purify it. Clear rivers and lakes may look clean, but there are millions of organisms in fresh water. If you don't purify it, you can get extremely sick from bacteria or viruses. Freshwater springs can be safe to drink from without filtering, but in a survival situation you should err on the side of caution.

LifestrawThe Lifestraw is a portable filtration device that lets you safely drink directly from any fresh water source. It's about 11 inches long, less than 1 inch around, and looks like a jumbo drinking straw. One end has the narrow mouthpiece, the other goes directly into the water source. Each Lifestraw lasts 700 liters, roughly the amount of water needed for one person per year. The filter gets rid of nearly 100 percent of waterborne bacteria, 98.7 percent of viruses and removes particles as small as 15 microns. Five million people per year die from waterborne illness -- mostly children. More than a billion people worldwide have no access to safe drinking water. The makers of Lifestraw hope to help cut this amount in half by the year 2015. You can donate money through two organizations to help provide Lifestraws to people in need all over the world at the Lifestraw Web site.­ ­Lifestraw is also a great item for any outdoor enthusiast to have in his or her emergency survival kit. It weighs only 140 grams and it just might make the difference in your chances of survival.

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In this article, we'll take a look at different ways you can find or collect safe drinking water in the wild.­

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