Merck Manual

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Quick Facts

About Body Water

By

The Manual's Editorial Staff

Last full review/revision Jun 2020| Content last modified Jun 2020
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About half your body weight is water. So if you are a 160-pound woman, you have about 80 pounds (10 gallons) of water in your body.

You need the right amount of water in your body for good health. Either too much or too little can cause serious problems.

The water in your body contains electrolytes. Electrolytes are minerals, such as sodium and potassium, that help with many important body functions. Your body needs the right balance of electrolytes.

  • Your body works to keep the amount of water and electrolytes in your blood steady

  • Sweating, throwing up, and having diarrhea all make you lose a lot of water and electrolytes quickly

  • Too little water in your body is dehydration

  • Too much water in your body is overhydration

  • When your body needs more water, your brain signals that you're thirsty

  • When your body has too much water, your kidneys make more urine so you pee it out

  • Most of the time, you can drink enough to make up for fluid you lose

How does your body balance the amount of water?

Your body constantly balances how much water and electrolytes you have.

When your body needs more water:

  • Your brain makes you feel thirsty so you’ll drink more

  • Your brain also signals your kidneys to make less urine, so water and electrolytes don't leave your body

When your body needs less water:

  • Your brain signals your kidneys to make more urine

What can throw off my body's water balance?

Most of the time, your body does this balancing act automatically. You don't have to think about it. It's not necessary to force yourself to drink when you're not thirsty.

However, if you lose a lot of water very quickly and don't have a way to replace it, you can have trouble. Also, certain diseases that affect your brain or your kidneys can throw off how your body balances water and electrolytes.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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