The Fatigue Fighter: Next time you’re feeling drowsy, chug a glass of cold water for an instant fix. Then, take a look at how much water you’ve been drinking. According to Dr. King, you should aim to drink half your body weight in ounces of water every day. If you weigh 150 pounds, that’s 75 ounces of water (about 9 cups). If you want something more pleasing to your palate, snack on watermelon, which is about 91 percent water.