Replacement approach. The average urine output for adults is 1.5 liters a day. You lose close to an additional liter of water a day through breathing, sweating and bowel movements. Food usually accounts for 20 percent of your fluid intake, so you if you consume 2 liters of water or other beverages a day (a little more than 8 cups), along with your normal diet, you can replace the lost fluids.
Eight 8-ounce glasses of water a day. Another approach to water intake is the "8 x 8 rule" drink eight 8-ounce glasses of water a day (about 1.9 liters). The rule could also be stated, "drink eight 8-ounce glasses of fluid a day," as all fluids count toward the daily total. Though this approach isn't supported by scientific evidence, many people use this basic rule as a guideline for how much water and other fluids to drink.
Dietary recommendations. The Institute of Medicine recommends that men consume 3 liters (about 13 cups) of total beverages a day and women consume 2.2 liters (about 9 cups) of total beverages a day. These guidelines are based on national food surveys that assessed people's average fluid intakes.
I drink anywhere from 3 to 4 liters of water a day. I dehydrate easily, so I keep my fluid intake up. Also, I only drink water. No sodas, no teas.