In the drink: do we really need 8 glasses of water a day?

“Drink eight glasses of water a day.” We’ve heard the advice to drink 8 X 8 (eight 8-ounce glasses) for years, even though few of us manage to down that much. How did it start? And what’s the evidence to back it up? To find out, we talked with an internationally recognized expert on water balance and the kidneys.