It's the myth that just won't go away. Almost everyone thinks they don't drink enough water, but the idea that we all should drink lots of it - eight glasses per 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 (NRC) that adults should consume 1 millilitre of water for each calorie of food, which adds up to about 2.5 litres per day for men and 2 litres for women. According to Barbara Rolls, a nutrition researcher at Penn State University and author of the 1984 book Thirst, this amount is about right for people in a temperate climate who aren't exercising vigorously. And 1.9 litres is what you'll get from drinking eight 8-ounce glasses of water - the 8×8 rule - as per the US version of the myth.
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