How long can humans last without water?

June 29, 2006 5:28 AM

How long can a reasonably healthy human survive without water?

I'm trying to find credible, reliable sources that tell me the maximum amount of time a person can survive without any hydration whatsoever. I realize this varies person to person and depends on factors like heat, shelter, etc., but I'm looking for the maximum. Assuming no real medical treatment will follow the experience.

posted by Amizu to health & fitness (24 answers total)

The survival rule of thumb is: 3 hours without shelter, 3 days without water, 3 weeks without food.

This article suggests that an adult in comfortable surroundings can survive for a week with no or little water intake.
posted by pharm at 5:43 AM on June 29, 2006

The crew of the Lady Be Good made it for eight days.
posted by chef_boyardee at 6:07 AM on June 29, 2006

As a nutritionist, the figure for survival I've repeatedly heard is 48 hours without water and two weeks without food. Of course this varies on so many different factors, as others have pointed out. It should be noted though that it's not as if from the point when you stop consuming liquid, to the point that you die, you'll be able to function at full capacity. Death by dehydration is a nasty process involving incessent skin irritation, halucinations, and the swelling/ cracking of the tongue.
posted by Smarson at 6:15 AM on June 29, 2006

Wikipedia's average of three or four days seems a bit short, but maybe not if you figure in elderly people in hot climates, where life expectancy without water is a matter of hours. Also, digestion requires a lot of water, so if a person is not drinking, should we assume they are not eating, as well? Another big variable (which you explicitly recognize) is whether the person doing the surviving has shelter, or at least reasonable clothing, including a hat, which could vastly decrease perspiration loss, extending survival significantly.

This U.S. Forestry Service survival training guide [MS Word .doc file] suggests 3 days without water is a serious threat to survival. Your assumption that no medical treatment will follow means that a person in such circumstances will have to rehydrate orally, so that they can not afford to get into the last stages of dehydration where the chemistry and mechanics of the digestive or urinary tracts may be seriously affected, or where water seeking behaviors and rationality itself may be compromised. Therefore, I will argue that this, more than the limit cases of physiology determine survival. [The Lady Be Good crew did not survive, and apparently died traveling, which is not the best water conservation strategy.] If you can't safely risk delusional states (you're alone, you have to do some set of tasks to end the situation causing the water problem, etc.), you have to be competent to judge your state right up to the point of taking action, and that's your survival limit.
posted by paulsc at 6:25 AM on June 29, 2006

Pharm's "3 hours without shelter" seems very low to me...
posted by ruwan at 6:50 AM on June 29, 2006

Pharm's "3 hours without shelter" seems very low to me...

Yeah, maybe in the desert, with the sun beating down on you, but otherwise, I'm pretty sure I've gone several hours without shelter.
posted by scottreynen at 7:00 AM on June 29, 2006

Thanks for the responses! A little more info.... The person wouldn't be eating either. He would be in shelter, wearing clothing, though in a hot climate without electricity. He would otherwise be young and in good health. After the ordeal he would have access to home remedies, but no IV, no rehydration salts, etc. I'm mostly wondering what the maximum time he could do this would be, without dying or being severely incapacitated afterwards.

I've heard the 3-3-3 rule before, but it seems more like a guideline for safety, and less like the absolute maximum a healthy person could endure and still survive such an ordeal....
posted by Amizu at 7:00 AM on June 29, 2006

ruwan writes "Pharm's '3 hours without shelter' seems very low to me"

Realistic in adverse conditions but I've spent much more time than that on the beach.
posted by Mitheral at 7:07 AM on June 29, 2006

Death by dehydration is a nasty process involving incessent skin irritation, halucinations, and the swelling/ cracking of the tongue.

Headaches, anxiety attacks, confusion, blurred vision ... severe dehydration sucks.
posted by spaceman_spiff at 7:17 AM on June 29, 2006

The survival rule of thumb is: 3 hours without shelter, 3 days without water, 3 weeks without food.

...the one I've always heard was 3 minutes without air, 3 days without water, 3 weeks without food.
posted by Jairus at 7:19 AM on June 29, 2006 [1 favorite]

seems like you could ask this guy.
posted by nimsey lou at 7:21 AM on June 29, 2006

I'm looking more for medical reports, or something from the medical/survival community saying that "x" days is the absolute maximum. Maybe it's not out there since there's so many variables, but at least something like an average number of days for a reasonably healthy person in decent conditions.... I mean, skin divers can go without oxygen for longer than 3 minutes, but maybe 3 minutes is accurate for a reasonably healthy person with no other adverse factors.
posted by Amizu at 7:27 AM on June 29, 2006

I'm quite sure you could wander the Sahara naked for three hours and live.

Now 3 hours in the Artic naked may be different. But with good clothing it should be possible. I don't buy the 3 hours without shelter bit.
posted by DieHipsterDie at 8:26 AM on June 29, 2006

I've also heard the 3-3-3 rule as "3 minutes without air, 3 days without water, and 3 weeks without food." Whether I heard it from a reliable source or an episode of CSI, however, I'm not sure.
posted by Godbert at 8:41 AM on June 29, 2006

Now 3 hours in the Artic naked may be different. But with good clothing it should be possible. I don't buy the 3 hours without shelter bit.

3 hours without shelter is both silly and plain wrong. Ask a homeless guy.
posted by Jairus at 9:00 AM on June 29, 2006

A lot of the reason for the confusion is that it depends on what you mean by "survive". If you mean "still breathing at the end" then it's possible for most people to go up to a week.

It also varies by person, and it depends enormously on the situation (e.g. the ambient temperature).

And if someone goes a week without water, it's unlikely that they would recover fully. There's likely to be permanent damage to the major organs.

I think the point of the "3 day" period mentioned above by many is that after 3 days, nearly everyone will still be breathing, and if water was then supplied there would be no long term consequences. But once you go beyond 3 days, it starts getting nasty.
posted by Steven C. Den Beste at 9:59 AM on June 29, 2006

The proper adage is indeed "minutes without air." If you're stuck without shelter in the sort of adverse conditions that can kill, you're going to be dead long before three hours pass.
posted by cribcage at 10:01 AM on June 29, 2006

I don't buy the 3 hours without shelter bit.

My outdoor survival training has taught me a rule of thumb like this. But you are all misunderstanding what the world "shelter" really means in that context. It is talking about protection from the elements. So shelter includes clothes, tents, houses, cars, hats, sunscreen, etc. When I go hiking in the Rockies, I always have the shelter to survive out there for days, if need be. I don't ever take a tent hiking. In the summer in most parts of America, the clothes on your back are enough shelter to survive in the wild until mid-Fall.

And they just chose 3 as a mnemonic device. Shelter comes first, as you need it badly unless you are on a temperate, tropical island. In the arctic you will have minutes without shelter (meaning, you were out there naked). Most places you'll last much longer, especially when you assume most people have at least some "shelter" with them when they end up in a survival situation. But 3 hours is given because, if you are in a survival situation, you need protection from the elements, and you might not be able to get it if you don't get it fast, as your mental condition will deteriorate rapidly if you are hypothermic or starving or getting heat stroke or dying of thirst or what not.
posted by teece at 10:15 AM on June 29, 2006 [2 favorites]

Terry Schiavo lasted thirteen days without food or water. Her tube was removed March 18, 2005 and she died on March 31, 2005.
posted by NortonDC at 10:45 AM on June 29, 2006

Also, digestion requires a lot of water, so if a person is not drinking, should we assume they are not eating, as well?

We should forbid eating, but for the opposite reason: Hydrocarbons and fat produce water when digested. A camel gets along fine in the desert by just consuming the fat it carries on its back, producing both the energy and the water it requires.
posted by springload at 11:16 AM on June 29, 2006 [1 favorite]

That rule of 3s counts appropriate clothing as "shelter". It's kind of worked stupidly.
posted by fshgrl at 12:39 PM on June 29, 2006

The record for survival without food or water is 18 days.

(check the very, very bottom of the article)
posted by storybored at 1:20 PM on June 29, 2006

IANAD (I Am Not A Doctor), JARID (Just A Random Internet Dude), but I had a couple of other thoughts on this topic, based on the additional scenario tips above from Amizu. First, a person that is apparently young and healthy when in normal condition can degrade faster than average due to dehydration, if, say, his electrolyte balance gets upset to the point of setting off underlying, but normally not symptomatic conditions, such as heart arrhythmia. Here's a bunch of technical literature about the effects of various degrees of dehydration, but the basic point I'm trying to make is that a supposedly healthy person pushing themselves into dehydration has no guarantee that they will only suffer gradually increasing symptoms directly related to fluid loss, or that the way back will be as simple as just adding water and salt. As far as I know, there's no way to know for sure if you are one of those healthy but susceptible types until your electrolyte balance goes whacko, so lotsa luck taking maximums as any kind of planning guide.

Keeping your blood and extracellular fluids exactly in balance while you dry out a lot, and then get back to normal is no mean feat, and the process can go uncontrollably south in hours or even minutes if by bad luck you get a little too far out of whack, especially at the dry end of the scale, when your blood is thicker, your kidney function down to nothing, your ticker weak, and your brain irritable and befuddled. Again, I'm just trying to get across the point that a person doing this under the conditions set forth by Amizu is essentially being his own doctor, and as such, would reasonably need to begin rehydration well before he got to a state of incapacitation, so as to meet the condition "without dying or being severely incapacitated afterwards." As most survivalists know, surviving generally means protecting your reserves wherever possible, not pushing yourself to extremes, where capacities are slim and judgement variable. A person whose body is pushed the raw edge of endurance isn't surviving, he's just lucky a little longer...

Terry Shiavo died. The Lady Be Good crew all died. People going more than a week without any water generally require extensive medical intervention to have any chance of survival, and often do not completely recover. This is not the condition Amizu is talking about.
posted by paulsc at 2:41 PM on June 29, 2006

The three hours without shelter thing is partially a mnemonic, but as described by teece it's including all the things that provide shelter — clothing, location, etc etc. It also assumes a northern temperate climate, where the temperature falls significantly at night. Obviously other environments bring varying times.

Given the large number of variables involved, it's really just a reminder that shelter is more important than water in a survival situation: The environment can kill you before dehydration does.

One of the reasons for this (will have to look up the reference for this) is that in a no-food survival situation, it takes about 24 hours for your body to switch over to full 'burning reserves' metabolism. In the interim, you can be very low on energy and are much more susceptible to environmental challenges.
posted by pharm at 12:05 PM on July 1, 2006