Do you drink eight glasses of water per day? Or at least try to? Then a question for you – what is a glass of water?

If you are a regular reader of this blog, your reply might be along the lines of “it is a container largely formed from silicon dioxide which is used to hold a non-specific volume of dihydrogen monoxide.”

However, more specifically, what is the size of the glass container that contains the water?

I wondered this a few years ago when pondering that I might want to switch from coffee in the afternoons to water, and thinking about the claim that a person should drink 6 to 8 glasses of water per day, I wondered how large should a glass of water be.

Are the glasses I have in my kitchen the approved size, or is the size of glass the medical advice based on closer to the water cooler cups used in offices, which would mean I only need to drink 4 of my glasses of water to meet the recommended intake.

I wanted to know.

Guess what – there is no standard size for “a glass of water” in medical terms. In fact, the claim that we should drink 6 to 8 glasses of water per day has absolutely no basis in medical science whatsoever. As it happens, no one is really sure where the claim came from, although some reports I read at the time (but can’t find today) suggested it was an “off the cuff” comment by a senior US doctor about 60 years ago to give an answer to an unexpected question from a journalist.

I was reminded of the issue this morning, as I was scanning my science press releases and came across this one from a doctor writing a “link bait” article in the British Medical Journal.

Undeniably most of us feel better if we drink plenty of water during the day, and I find drinking cold water – I keep a jug of tap water in the fridge – helps me to concentrate in the afternoon, but that could be just a placebo effect reinforced by our presumption that we should be drinking water to stay healthy.

But there is no evidence for it.

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4 Comments

  1. Kit Green

    Wine is better, but I cannot find the article that told me it was one of my five a day (or more on some days).

  2. Giles Williams

    The best advice I’ve had is to drink enough to remain adequately hydrated, evidenced by your urine being pale and clear. The amount of clear fluids taken in to do this will vary from person to person.

    ie. Measure outcomes.

  3. Mark

    Two of my water-spurning brothers suffer from kidney stones, so I have always attributed my so-far unsedimented internal hydraulics to the mass quantities of ice water I drink (the brothers prefer sodas). Of course, I have always lived in desert climates, where you need to intake a great deal of liquid to, um, live.

  4. Martin Tolley

    http://www.wateraid.org/uk/ says a glass is 250 ml. The site has a nifty calculator based on your weight and daily exercise time. According to them my grossly over-weight and under-exercised body requires just north of 6 old imperial pints a day, or around 2200 pints a year! Beer is mostly water isnt it?

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