You Need to Drink Eight Glasses of Water a Day
"The widely repeated health rule that everyone should drink eight 8-ounce glasses of water daily."
The number traces to a 1945 recommendation from the US Food and Nutrition Board, which suggested about 2.5 litres of water intake a day, roughly eight glasses. Crucially, the same recommendation explicitly noted that most of that amount is already contained in ordinary food, a detail that appears to have been dropped as the advice got passed along, leaving only "drink eight glasses" behind. No actual research produced the specific 8x8 figure in the first place, and a review of 18 separate trials on the subject found a genuinely mixed picture, with about half showing a benefit and half showing none, and most studies too small or short to be conclusive either way.