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Why Your Body Needs Water 

Need a reason to drink water? Water is essential to good health—and life. Up to 60 percent of an adult’s body weight and about 74 percent of a newborn’s body weight is water, making it the largest single substance in the human body.

Here's what water does for you:

  • It helps carry nutrients to all the cells in your body.

  • It helps carry waste products from the cells.

  • It is a part of essential reactions within the body.

  • It helps regulate body temperature by absorbing heat generated by your metabolism and eliminating excess heat through sweating.

  • It helps with digestion of food.

  • It helps lubricate your joints.

Your body must balance the amount of water lost with the amount it gets from food and beverages. About 80 percent of the water you take in comes from the water and beverages you drink; the remaining 20 percent comes from food. A small amount of water also is produced when your body metabolizes foods.

How much water do you need? That depends on your age, percent of body fat, general health, diet, temperature of the air around you and your level of activity. You lose water through urine, sweat, feces, and the air you exhale.

The Institute of Medicine (IOM) suggests that the average healthy woman drink about nine cups a day of liquids, and the average man about 13 cups a day.

Dangers of dehydration

Usually, your body balances the amount of water you consume with the amount of water eliminated. The organs mainly responsible for this balance are the kidneys. They do this so well that the amount of water in your body does not change more than 0.2 percent of your body weight over a 24-hour period. Certain circumstances such as prolonged physical activity, high air temperatures, high fever, diarrhea, trauma and burns increase the amount of water lost. If you don't replace that water, you become dehydrated.  

Dehydration can influence your mental functioning, your heart rate, and your ability to regulate body temperature and blood pressure. If you lose even 1 percent of your body weight in water, your physical performance is affected and you feel tired. If you lose 2 to 4 percent, your mental functioning is affected; a loss of more than 10 percent of your body weight is a medical emergency and if not reversed can lead to death.

Infants, young children, people with certain chronic health problems and elderly adults are more susceptible to the effects of dehydration.

You can become dehydrated by not consuming enough fluid from foods and beverages. These are conditions that also can make dehydration more likely:

  • Sweating during exercise that is not compensated by drinking extra fluids; exercise even in cold weather can cause sweating

  • Hot, humid weather

  • High altitude, which causes raid breathing and increased urine output

  • Illnesses such as poorly controlled diabetes, and illnesses that cause vomiting, diarrhea, or fever

  • Pregnancy

  • Certain medications

Each of these conditions alone can contribute to dehydration; a combination of them can cause it more quickly.

Although caffeine does cause you to urinate more frequently, the effect is short-term and does not typically cause dehydration. Both caffeinated and non-caffeinated beverages can be used as sources of water.

Alcoholic drinks also can make you urinate more frequently, but, like caffeine, this increase is short-term and usually does not cause dehydration if you drink in moderation.

If you eat a high-fiber diet, you will lose more water through feces, but not enough to cause dehydration. A high-protein diet requires slightly more water to remove waste products created by the extra protein. The extra fluid lost in this process does not cause dehydration under normal circumstances, but it may increase dehydration in athletes who limit their fluids in order to lose weight.

Symptoms of dehydration

  • A dry or sticky mouth, caused by too little saliva

  • Less urine than normal, or no urine for eight hours. Urine that is darker than usual may indicate dehydration; diet, medications, and vitamin supplements can also affect urine color.

  • Few or no tears

  • Sunken eyes

  • Dry, cool skin

  • Fast heart rate

  • In infants, a sunken fontanel, the soft spot on the top of the head, may mean dehydration.

  • Lethargy, irritability or fatigue

  • Listlessness or coma; this is a sign of severe dehydration.