A、Loss of weight. B、Providing toxins. C、Loss of energy. D、Providing nutrients. C录音指出了脱水症状，哪怕轻度脱水也会导致精力不济(drain your energy)，身体虚弱

How much water should you drink each day? It’s a simple question with no easy answers. Studies have produced varying recommendations over the years, but in truth, your water needs depend on many factors, including your health, how active you are and where you live. Although no single formula fits everyone, knowing more about your body’s need for fluids will help you estimate how much water to drink each day.
    Water is your body’s principal chemical component and makes up about 60 percent of your body weight. Every system in your body depends on water. For example, water flushes toxins out of vital organs, carries nutrients to your cells and provides a moist environment for ear, nose and throat tissues.
    Lack of water can lead to dehydration, a condition that occurs when you don’t have enough water in your body to carry out normal functions. Even mild dehydration can drain your energy and make you tired.
    Every day you must replenish its water supply by consuming drinks and foods that contain water. So how much water does an average, healthy adult living in a temperate climate need? In general, doctors recommend 8 or 9 cups. Here are the most common ways of calculating that amount:
    First, 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. The rule could also be stated, "Drink eight 8-ounce glasses of fluid a day," as all fluids count toward the daily total. Although the approach really isn’t supported by scientific evidence, many people use this easy-to-remember rule as a guideline for how much water and other fluids to drink.
    Second, dietary recommendations. The Institute of Medicine advises that men consume roughly 3 liters of total drinks a day and women consume 2.2 liters of total drinks a day.
    Even apart from the above approaches, if you drink enough fluid so that you rarely feel thirsty and produce 1.5 liters or more of colorless or slightly yellow urine a day, your fluid intake is probably adequate. If you’re concerned about your fluid intake, check with your doctor or a registered dietitian. He or she can help you determine the amount of water that’s best for you.
20. What can help people estimate their water needs every day?
21. What condition can mild lack of water lead to?
22. What can people do if they are concerned about their fluid intake?