Drink 8 glasses of water a day

I’m not sure where I heard this first, but I’ve heard it a lot: you should drink 8 glasses of water a day to avoid dehydration. And it sounds very believable. We all know that we need water to live, and that the human body is mostly water (95% by weight, in fact; it’s a wonder we’re not tidal). I think we all suspect that water would be better than soda or coffee or whatever else we’re drinking. And 8 sounds so tangible.  I’ve known a number of colleagues and friends who have carried around measured bottles or tumblers to get their recommended dosage of the clear stuff.  They’re smart people.

I bet I’m not alone in having vague beliefs about water, without quite being able to place the source, such as that drinking more water will make your skin clearer, or reduce insomnia, or help you lose weight, or make us think more clearly, or reduce the likelihood of some illness or other… though I can’t actually remember what illness.

And I’m sure there’s truth in there. I think we could all stand to drink more water and less of everything else, especially all the sugars in soda and juice – pointless calories that are processed by the body into pure diabetes (there may be some in-between steps, I’m not a doctor).

But over the years I have learned to be suspicious of things people commonly think to be true. “Wisdom of the crowd”? More like the “dumbsdom of the crowd”, laugh out loud. OK that doesn’t work, but the point stands. People have an awkward habit of believing things because enough other people believe it such that that it reaches critical en masse. Because it feels truthy, and because it’s memorable.

I’m also suspicious of this particular claim because it reminds me of the tragic story of Leah Betts, who was all over the news when I was 16, and highly formatively influentiable. She took an ecstasy tablet and died, and Britain’s newspapers just jumped on it as an example of the dangers of drug taking and the decline of moral standards and that evil drug dealers are coming for our middle class children, or whatever other moral panic would sell papers at the time. I was pretty innocent back then (and I suppose still am, having not taken any illegal drugs except perhaps drinking when I was 17) but even my computer-club friends and I were savvy enough to see that this was palpable bullshit. The fact that this one case made the front pages of all the newspapers only highlighted how obviously rare it was. Also the fact that eventually surfaced that the MDMA hadn’t actually killed her, water had. That’s the bit of information that sticks with me, and that’s why it springs to mind when I hear this “8 glasses” thing.

Leah had taken a pill then presumably panicked a bit and heeded the advice of well-meaning anti-drug advisories that “ravers” (sigh) should drink water to avoid becoming dehydrated. Unfortunately she’d drunk 12 pints (7 litres) of water, which resulted in something called water intoxication, ultimately killing her. I’m guessing water killed way more people than ecstasy that year. Just lacks a certain newspaper-selling quality, and isn’t quite so dramatic on billboards.

I’m not saying that we should all immediately replace all water in our diet with illegal drugs. I mean you can if you want to, I’m not the boss of you; but I would caution against it (and if you decide to, let us know how you get on in the comments section). Still, it’s one of the reasons I’m slightly cynical about commonly held medical beliefs without apparent evidence (I’m looking at you, homeopathy and the anti-vaccine movement). In this case I blame the Evian lobby. Big Water, getting all up in our plumbing.

So I spent a week drinking 8 glasses of water a day, and did some digging around the health benefits.


First thing’s first: 8 glasses is a lot.  Sometimes it’s written as 8 cups.  Turns out that means pretty much the same thing – a cup is a little over 2/3rds of a tall glass so if you’re not filling to the top, there’s not much in it. Either way, it’s a lot of water. I found myself a larger glass that held about 2 cups, and fell into a routine of drinking one with breakfast, one with lunch, one with dinner and one last thing at night because I’d consistently forgotten about it until I went to bed. On the Thursday I forgot a glass and had to drink 5 the next day, all the while wondering when water intoxication kicks in.

Lessons learned? You’re going to be getting up a lot in the night. That’s it. No health benefits, no shiny clear skin, no better sleep… I couldn’t really find any benefit. I am not saying it is without benefits, and I am almost certain that I drank fewer unhealthy drinks that week, which probably lowered my calorie intake and gave me another day into old age with my real teeth. But nothing was apparent.

Meanwhile, it turns out it’s really easy to debunk this whole “8 glasses” thing. In fact the first two results from a Google search for “8 glasses of water” are two of my go-to sites for urban myths and statistics, respectively: Snopes and FiveThirtyEight.

FiveThirtyEight points to a National Food and Nutrition Board statement:

A suitable allowance of water for adults is 2.5 liters daily in most instances. … Most of this quantity is contained in prepared foods.

So turns out the whole thing is a myth after all. 8 glasses is an arbitrary and likely inflated number, and you should just drink when you’re thirsty. One other major lesson, courtesy of Snopes: all drinks count towards your intake of fluids, including caffeinated ones.

the idea that one must specifically drink water because the diuretic effects of caffeinated drinks such as coffee, tea, and soda actually produce a net loss of fluid is erroneous

They go on to explain why, with sources, so head over there if you care to read the details.

As for me, while this wasn’t particularly worthwhile, I’m not completely done with this water thing. Another week, I’ll try drinking only water, and I may also give the idea of drinking a glass of water before meals a go, as a way to reduce appetite and therefore eat less. I think both could be quite healthy things to do. But I’m happy to drop the arbitrary and unnecessary 8 glasses thing.

  • Difficulty: Mild
  • Worthwhiliness: Low, except as a way to reduce your consumption of other, less healthy drinks.

Header image by Derek Gavey

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