Do you drink 6 to 8 glasses of water per day?

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.