【概括大意】A good rule of thumb(好的做法)is to take your body weight in pounds and divide that number in half. That gives you the number of ounces(盎司)of water per day that you need. For example, if you weigh 160 pounds, you should drink at least 80 ounces of water per day. If you exercise you should drink another 8-ounce glass of water for every 20 minutes you are active. If you drink coffee or alcohol, you should add at least an equal amount of water. When you are traveling on an airplane, it is good to have 8 ounces of water for every hour you are on board the plane.
The main idea of this paragraph is__________.