You’ve probably heard that you need to drink 8 glasses of water a day – 9 to 13 if you exercise. Here’s where the number comes from: You typically lose about 10 cups of water per day – 2 cups to sweating and evaporation, 2 cups to breathing, and 6 cups to waste removal. You can replace up to 2 cups through the water in the foods you eat but you have to make up the remaining 8 cups by drinking fluids, water being the best choice. Recent research suggests that you need a much higher fluid intake, from 3 to 6 quarts per day (and because there are 4 cups in a quart, that’s 12 – 24 cups per day). The low end is if you’re eating lots of fruits and vegetables (and you are, aren’t you?), because those foods are high in fluids.