One brain region combines signals from your mouth, gut and bloodSerious question: How much water does the average adult need to drink every day? You've probably heard the usual answer: eight 8-ounce glasses, sometimes stated as 8 × 8. But there's not much science behind this ubiquitous recommendation. A 2002 research review found essentially no reliable studies. Any truly serious answer to the how-much question will begin with some version of “it depends.” Are you in a hot location? Are you exerting yourself? Are you in good health? How big are you? Do you eat a lot of salty foods, or do you load up on fruits and vegetables?We do need water every day, but the average person gets it from many sources: tea or coffee, soft drinks (which often include sugar that you don't need), and food. “We typically get about 20 percent of our fluid requirements from solid foods and about 80 percent from beverages,” says Brenda M. Davy, professor of human nutrition at Virginia Tech University.