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Is there a formula which can be used (I'm thinking one that gives amount of water needed factoring in time or distance covered and temperature) to roughly work out the amount of water that needs to be carried for a particular hike?

Obviously this will be a very rough guide - I know how much I generally drink, but I tend to drink quite a lot, I'm wondering as a rough approximation I can give to others to form an idea in their head.

Is there an "official" such formula, or have others coined their own that they use?

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3 Answers 3

up vote 12 down vote accepted

The rule is 3 liters per person per day. You may get away with 2 liters if it's not too hot and you stay moderate. Keep into account that your "normal day" intake is skewed by the contribute brought from food. If you eat food with less water in it, which is likely during a hike, your need for actual water is higher than the one you experience in your daily life. Add the physical activity and you get the idea.

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This is the same rule I use and have used reliably for ages now. –  Russell Steen Jun 2 '12 at 2:35
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+1 great general rule. One thing I would add is to know the humidity of where you are. I live in the VA/NC region and when I took a trip backpacking in New Mexico I had to consume an extra liter a day at the least. –  Justin C Jun 6 '12 at 15:05
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-1 because I don't believe it's possible to give a general rule. 3 liters is too much for some conditions and too little for others. Also, how much you need to drink is completely different from how much you need to carry. The amount you carry can often be zero, if the water is plentiful and (as is usually the case in the backcountry) safe to drink without treatment. –  Ben Crowell Jan 20 at 19:51

The answer to this question depends completely on the weather and on how plentiful water is on your route. In the Sierra, the answer is typically zero, i.e., there is almost never any need to carry any water on your back. (Nor is there any need to purify water in the Sierra; see http://outdoors.stackexchange.com/a/4058/2169 .) When you're thirsty, you stop at the next stream, lean down and scoop up some water, drink it, and then continue hiking. There is the myth that "thirst is too late," i.e., that you have to drink lots of water because you'll be dangerously dehydrated by the time you actually feel thirst; this is an urban folk tale.

If you're in a different environment, such as a hot desert, the answer could be totally different. For example, temperatures in the low-elevation areas around Palm Springs, California, have been recorded as high as 50 C (120 F). In these conditions, the amount of water you need is infinity. That is, your body's ability to cool itself is simply overwhelmed, and you may die no matter how much water you drink, if you're outside in the hot sun at midday. In this kind of heat a few years ago, one hiker was found dead, sitting peacefully on a rock, 100 meters away from a tennis court, with a full water bottle in his hand.

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So your formula/estimation is "between zero and infinite"? You have to be a physicist ;) That being said, your answer obviously is correct but not THAT helpful tbh. –  EverythingRightPlace Jan 20 at 20:41

I walked Hadrian's Wall recently carrying an 18kg backpack. It was hot, sunny weather for six of the seven days. I had a 2 litre bladder of water and by the end of each day I had ran out of water. That was not a nice feeling walking the last couple of miles without water. I have now upgraded to a three litre bladder.

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