Don't swallow that myth!

08 September 2013 - 02:02 By The New Scientist

IT is the myth that just will not go away.

Almost everyone thinks they do not drink enough water, but the idea that we all should drink lots of it - eight glasses a day- is based on no scientific data whatsoever.

No one really knows where the eight-glasses idea comes from. Some blame the bottled water industry, but plenty of doctors and health organisations have also promoted it over the decades. The source might be a 1945 recommendation by the US National Research Council that adults should consume 1ml of water for each calorie of food, which adds up to about 2.5 litres a day for men and two litres for women.

What most people do not realise, though, is that we get a lot of that water from our food. Foods contain water and are broken down chemically into carbon dioxide and more water. So if you are not sweating buckets, you need only about a litre a day.

But any talk of glasses is misleading because there is no need to drink pure water. The fluids that people drink anyway, including tea and coffee, can provide all the water we need, says Heinz Valtin, a kidney specialist at Dartmouth Medical School in Lebanon, New Hampshire.

According to the myth, caffein-ated drinks do not count because they are diuretic. Not true: a comparison of healthy adults in 2000 found no difference in hydration whether they got their water from caffeinated drinks or not.