Several years ago I found an article online about a researcher who debunked the eight glasses myth. Since then, I've tried and tried to find it again. Finally, here's a reference to it!
From the Web site of the British Medical Journal, a publication of the British Medical Association:
Revealed: The seven great "medical myths"
Fri Dec 21, 2007 10:19am ET
An excerpt of the article:
People should drink at least eight glasses of water a day
The advice to drink at least eight glasses of water a day can be found throughout the popular press.w1-w4 One origin may be a 1945 recommendation that stated: A suitable allowance of water for adults is 2.5 litres daily in most instances. An ordinary standard for diverse persons is 1 millilitre for each calorie of food. Most of this quantity is contained in prepared foods.w5 If the last, crucial sentence is ignored, the statement could be interpreted as instruction to drink eight glasses of water a day.w6
Another endorsement may have come from a prominent nutritionist, Frederick Stare, who once recommended, without references, the consumption "around 6 to 8 glasses per 24 hours," which could be "in the form of coffee, tea, milk, soft drinks, beer, etc."w7
The complete lack of evidence supporting the recommendation to drink six to eight glasses of water a day is exhaustively catalogued in an invited review by Heinz Valtin in the American Journal of Physiology.w8 Furthermore, existing studies suggest that adequate fluid intake is usually met through typical daily consumption of juice, milk, and even caffeinated drinks.w9 In contrast, drinking excess amounts of water can be dangerous, resulting in water intoxication, hyponatraemia, and even death.