How to Spot a Psychopath

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?

Lana

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.