All I do is drink and wee, I'm gonna live forever!

A reader writes:

Seeing lrwiman's comment on your post about how you can't lose weight by eating ice reminded me: Do you really need to drink eight glasses of water a day?

I guess it actually depends on who "you" are, how big or small, and how much you sweat and so on. Is eight 8-oz glasses just a one-size-fits-most amount for everyday urban humans?


There is no scientific basis for the "eight glasses a day" idea.

Eight eight-fluid-ounce glasses add up to, of course, 64 fluid ounces, or about 1.9 litres. That is rather a lot. If you're an office worker, you are very unlikely to need that much water (or equivalent other liquids, though the people who support the eight-glasses thing often say that no beverage other than water counts at all) to be perfectly hydrated. If you're a labourer in a hot climate, though, you're going to need a lot more than eight glasses.

(See also, people hiking in the desert who don't realise that you need to drink a lot more water, and keep your electrolytes up, when you're exercising in high temperatures and low humidity.)

Unless you drink a really amazingly large amount, it won't do you any harm to drink more water than you need, if you're not concerned about the amount of time you spend in the bathroom. 1.9 litres over several hours is well below the level needed to cause water intoxication in an adult, unless your kidneys are in bad shape.

Note that your total water intake can very easily be three or four litres a day, because other beverages, and water contained in food, count towards it as well. The eight-glasses people usually warn against consuming water when it's mixed with other substances that reduce its net hydrating effect, like caffeine or alcohol, which are both diuretics.

As usual, though, the dose makes the poison, or in this case the diuretic. A doppio ristretto or shot of Polish Pure Spirit is, like drinking seawater, going to have a net negative effect on your hydration. But if ordinary black tea didn't hydrate you, the entire British Empire would have died of thirst in about 1750. You can also remain well hydrated if all you drink is beer or weak wine; beer and diluted wine used to be staple beverages for whole cultures before the invention of sewer systems, when the available water was commonly contaminated with organisms that couldn't survive a few per cent of ethanol.

Drinking lots of water, often but not always this particular figure of eight glasses a day, pops up quite often as part of odd diet regimes.

The "Stillman diet", for instance, was an early low-carbohydrate diet which prescribed eight glasses of water a day in addition to any other fluid intake. And it sure did seem to pare away the pounds; it made a significant contribution to Karen Carpenter's downward trajectory of both weight and health.

Lorraine Day includes a lot of water-drinking in her list of things you can do to, immensely plausibly, cure yourself of cancer (unless of course you are Jewish, in which case she'd probably prefer that you die).

Back here on planet Earth, drinking water when you feel peckish can be a good dieting trick. Go ahead and throw in some ice cubes too, if you want something to (carefully...) chew on.

But apart from this, and from a few diseases for which drinking a lot of water is a treatment, there's no reason to drink water when you're not thirsty.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

9 Responses to “All I do is drink and wee, I'm gonna live forever!”

  1. Bern Says:

    We had "health assessments" in our office a few years back. The 'assessor' told me I was badly dehydrated, and needed to drink more water. Oh, really, I asked, are the 3-4 500ml glass-fulls I'm drinking per working day not enough?

    Turns out they were measuring 'hydration' via some sort of skin contact electrode. I suggested perhaps the cold, dry air-conditioned air might significantly reduce skin moisture, boost skin resistance, and screw up their readings - at which point they politely told me to go away...

    ...and drink more water, of course!

  2. Phil Says:

    Dennis Leary reference? I do approve!

    Personally, I've never subscribed to the whole "must be water only" school of rehydration. That's what my kidneys and (still functioning!) liver are for - filtration and metabolising.

  3. ix Says:

    Caffeine supposedly does not cause dehydration. This is the first hit on google

    I went through some of the articles cited a while back, they seemed legit.

  4. geobas1 Says:

    " when the available water was commonly contaminated with organisms that couldn't survive a few per cent of ethanol."

    in the case of wine I'd say this is spot on, but with beer the levels are not sufficient to kill off much of anything. what most people don’t' realize is brewers were pasteurizing long before that stuffy Frenchman figured out what the hell they were doing and it was given his name.

    • Synthetase Says:

      Sort of. Brewing beer involves boiling unfermented wort which will kill most organsims. The low pH of fermented drinks takes care of the rest (meaning organisms are likely to be present but they cannot grow and so their numbers are low). Pasteurisation doesn't usually involve boiling, especially when used with heat-sensitive liquids. It may mean holding a batch at 65 degrees C for half an hour or so. Also, Pasteur deserves some credit for disproving the spontaneous germination hypothesis and at least giving a reason why heat-treatment is useful.

  5. Jonathan Says:

    I first heard of the 8 glasses target from Elle MacPherson.

  6. DavidF Says:

    These guys have a lot to say on the subject of marathon runners being told to drink too much.

    Apparently the Kenyans drink very little, but they aren't out there very long.

  7. meerkat8472 Says:

    My mother was told by her doctor to cut back on her water intake because it seemed to be flushing her body of potasium (she showed extremely low potasium levels on several blood tests). I thought the low potasium could have been a symptom of something else, but her doctor didn't seem to think so. That was a while ago and cutting back a bit has seemed to help her. Oh and she wasn't even drinking eight glasses a day (though it was probably pretty close), she is a small woman though. Anyway, the point of this story is that some doctors obviously believe it can be harmful to drink too much water, and too much may be less than you think, or it may not I don't know.

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