The amount of water you should carry depends heavily on outdoor temperatures and varies from person to person, but the rule of thumb is: drink 1/2 to 1 quart of water per hour of hiking. On a hot day climbing up a mountain, your body can lose 1 - 2 quarts per hour from perspiration. It's pretty simple though, if you feel thirsty at all, drink.
If you want to take it one step futher, you can determine how much water you are losing during exercise. Weigh yourself before and after a hike or workout. Subtract about 7% from the difference in pounds (to account for the burned calories), then multiply by 16. That's more or less how many ounces of water you need to replace.
Treating Water with Household Bleach
If you are smart about choosing your water source, you could go for days, weeks, or even years without treating your water and never get sick. It's a gamble, but after spending a few days stepping over moose poop, or seeing a bloated dead animal floating in a water source, or worse yet, having to witness your friend doubled over with stomach pains and running off into the trees to decorate the foliage... anyway, what I'm trying to say is, here's how I treat my water.
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