Water is necessary to maintain a healthy body and a clear mind. In fact, about 60 percent of your body is water; so you must stay hydrated to function efficiently. How much water is enough? The Institute of Medicine recommends about 13 eight-ounce cups of fluid per day for men and nine for women— and even more if you live in a super-hot climate or are very physically active. Sounds like a lot, but rest assured, it adds up quickly — and although water is your best bet, all fluids count (including coffee, tea, and milk in your cereal, and even juicy foods like vegetables, fruits, and nonfat yogurt!).