In a situation where you don't know when you will find water again, is it better to ration the water you have over time (and ever increasing dehydration) or to drink it to quench thirst as soon as needed?

It seems like there would be a tradeoff between longevity and performance in choosing one or the other course of action.

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    I think it depends on things like how much salt is in you, how your kidneys are functioning and other stuff. If you're prone to urinate soon after drinking water, I might recommend taking a little at a time. If you're not thirsty at all, I wouldn't drink any until you are (or until you have other indicators of thirst, if you have an impaired thirst response). If you just ate a big salty steak, or are enormously thirsty, drinking more might be somewhat better. If you're on a hike and are tired and sweaty (and ridiculously thirsty), you might need more water than a little. – Shule Oct 9 '14 at 20:50
  • Also note that Ben Crowell is right about how you don't have to drink water before you get thirsty to stay hydrated. There are lots of popular water myths. Your brain knows when it's had enough (according to ). So, if it's complaining about all this water you have to drink to stay hydrated, you should probably drink less. The article seems to indicate that drinking water should be pleasurable. – Shule Oct 9 '14 at 21:17
  • @Shule: do you have a link to the proper study (not just the press release - I didn't find it on pubmed) – cbeleites Apr 17 at 11:24
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    Just a thought: rationing (so that you know you're running into dehydration) can possibly help only in situations where you have a good idea when help will arrive. And it would still require the ability to judge to the amount of water needed in order to keep dehydration at a level where you brain still works reliably. As emergencies are unusual, I'd think this is close to impossible. (We don't need guard here against drinking too much - this won't be the error in a situation where you debate on rationing) – cbeleites Apr 17 at 15:00
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    @cbeleites - and in this pseudo-dehydrated state your mental abilities will be compromised to an unknown extent - thus limiting your ability to accurately judge how much water to ration. – That Idiot Apr 17 at 15:30
up vote 16 down vote accepted

The literature is mostly pro-drinking and anti-rationing. Hopefully these sources will provide some details for you.

The U.S. Army survival manual does not recommend that you drink water only when thirsty, as this leads to under hydrating. Instead, water should be drunk at regular intervals.

Even in cold weather:

Don't take chances with hydration. Do not ration your water; it is better inside you than in your canteen or thermos. Push yourself to drink as much water as you can while on a wilderness trip or while stranded in the wilderness in a survival situation.

The usual advice to someone in an emergency situation in the wilderness is to stay put, so that it's easier for rescuers to find you. In this situation, performance isn't an issue.

There is a folk belief that "thirst is too late," and that people are commonly dehydrated without knowing it. If you believed that, then you might drink some of your water even if you didn't feel thirsty. The belief is false, however.

In reality, thirst is an extremely powerful physical sensation, and when you're actually dehydrated (not just thirsty), you will feel so thirsty that you will simply drink because the urge is so strong.

There is a referenced article on the subject at

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    I agree (at least for me personally) that thirst is an accurate and strong guidance - but doesn't your case report on Liebler's heat stroke imply that under certain outdoor conditions fatal misjudgement of the required amount of water needed (or, the amount of work possible under the given conditions including available water) does actually occur. Valtin2002 is about sedate healthy people in temperate climate and explicitly exclude physical work in the heat. This boils down to the obvious: you need to replace the water you loose by sweating and sweating is crucial for thermoregulation... – cbeleites Apr 17 at 12:34
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    So the emergency advise would translate the "perfomance is not an issue" to physical performance (as opposed to keep your brain working reliably) - including that physical output should to be adjusted so that water requirement is kept at a minimum. (I.e. in hot conditions get yourself into shade + as cool as possible while leaving easily visible signs for rescue to find you) – cbeleites Apr 17 at 12:55

I have a very simple reasoning about it. It's only based on personal experience, so don't regard it as absolute truth.

Your body needs a certain amount of water to be comfortable, say, N. Comfort here includes urination (removal of poisons from body) and sweating (removal of heat). If you drink N or more, the body will function well.

If you drink less than N, the body will adjust to the deficit of water; it will decrease urination (so unwanted stuff will accumulate in the body), and then reduce sweating (body temperature will rise, leading to bad mood and less-than-optimal physical power).

You can often tolerate these effects (e.g. in emergency; also in general, depending on your goal and attitude), so you should drink less than your "normal" need.

In additon, imagine that you decided to conserve your water and drink 80% of N during the day, and you accept the ill effects of doing so. If you temporarily exceed that plan, drinking e.g. 30% of N in a quarter of a day, the body will "use" the excess water for natural but undesirable functions (urination/sweating). So you should be careful about how much you drink, and not succumb to thirst easily.

The tradeoff between longevity and performance is not easy to resolve; I feel that if you are carrying your water on your back, the tradeoff is always to drink less than needed for optimal performance. Some people will surely disagree though.

  • I agree with all your point (including the last paragraph). Too little water == dehydration == bad, too much water == increased sweating and urination == bad. The body adjusts. – Vorac Oct 6 '14 at 14:16
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    Sweating is not something the human body does optionally to get rid of excess water. It is needed to get rid of excess heat. Not drinking in order to not sweat will not work unless you drink so few that you get into severe dehydration and head into heat stroke. (See Ben Crowell's linked post: heat stroke is a consideration) The other way round, you have far better chances: reduce the need to sweat, so you don't need that much water. – cbeleites Apr 17 at 11:22

When I took a wildlands firefighting course in Arizona, the instructor said that if you find yourself lost in the desert, you should not ration your water. People have died of thirst with water in their canteens.

For what it's worth, I will refer to a single event: the outdoorsman Aron Lee Ralston survived 127 hours rationing his water.

Aron Lee Ralston had access to only 350 ml (12 imp fl oz) of water for a period of 127 hours. He was 28 years old and he was trapped in a slot canyon in eastern Wayne County, Utah, USA, between April 26, 2003 and May 1, 2003.

According to his book, Between a Rock and a Hard Place, he rationed his water.

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    This answer would need some more information to be useful. Things that spring to my mind are "How much water did he have?", "Where did that happen?", "How was the climate when this incident happened?". Even then the answer's endangered to be only anecdotal and possibly cannot be generalized to other people and situations. – Benedikt Bauer Oct 5 '14 at 20:25
  • @Benedikt Bauer you are right, I will provide some more info. – Alessandro Jacopson Oct 5 '14 at 20:55
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    Average time one can survive without water is 100 hours. A healthy man in nice cool canyon away from sun doing nothing is supposed to live for those 127 hours. And those 350ml were a small helper. It hardly proofs anything. A valid scenario would be 10L and a month to survive. – Val Oct 10 '14 at 9:17
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    @Val I know the "Rule of 3" ( see for example… ) which says "3 days" without water, now 3 days are 72 hours which is more or less the same order of magnitude of your 100 hours. Do you have any source for your "average time" of 100 hours? – Alessandro Jacopson Oct 12 '14 at 11:56
  • It is worth mentioning Aaron Lee Ralston's book. It is a detailed description of a survival event and how he managed water is described in detail and was an important factor. The 3 days / 100 hours 'rules' are of course VERY VERY ROUGH examples. He was luckily in shade but in desert environment. Managing fluid intake as he did probably contributed to his ability to struggle out and get to hikers/rescuers while the search was only just starting. – gaoithe Mar 31 '16 at 12:11

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