How Much of Your Body Is Water?

Have you ever wondered how much of your body is water? The percentage of water varies according to your age and gender. Here's a look at how much water is inside you.

The amount of water in the human body ranges from 45-75%. The average adult human body is 50-65% water, averaging around 57-60%. The percentage of water in infants is much higher, typically around 75-78% water, dropping to 65% by one year of age.

Body composition varies according to gender and fitness level because fatty tissue contains less water than lean tissue. The average adult male is about 60% water. The average adult woman is about 55% water because women naturally have more fatty tissue than men. Overweight men and women have less water, as a percent than their leaner counterparts.

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How Much Water Is in the Human Body?

By Anne Marie Helmenstine, Ph.D.

The percent of water depends on your hydration level. People feel thirsty when they have already lost around 2-3% of their body's water. Being dehydrated by just 2% impairs performance in mental tasks and physical coordination.

Although liquid water is the most abundant molecule in the body, additional water is found in hydrated compounds. About 30-40% of the weight of the human body is the skeleton, but when the bound water is removed, either by chemical desiccation or heat, half the weight is lost.

Where Exactly Is Water in the Human Body?

Most of the body's water is in the intracellular fluid (2/3 of the body's water). The other third is in the extracellular fluid (1/3 of the water).

The amount of water varies, depending on the organ. Much of the water is in blood plasma (20% of the body's total). According to a study published in 1945 and still widely cited, the amount of water in the human heart and brain is 73%, the lungs are 83%, muscles and kidneys are 79%, the skin is 64%, and the bones are around 31%.

What Is the Function of Water in the Body?

Water serves multiple purposes:

• Water is the primary building block of cells.
• It acts as an insulator, regulating internal body temperature. This is partly because water has a high specific heat, plus the body uses perspiration and respiration to regulate temperature.
• Water is needed to metabolize proteins and carbohydrates used as food. It is the primary component of saliva, used to digest carbohydrates and aid in swallowing food.
• The compound lubricates joints.
• Water insulates the brain, spinal cord, organs, and fetus. It acts as a shock absorber.
• Water is used to flush waste and toxins from the body via urine.
• Water is the principal solvent in the body. It dissolves minerals, soluble vitamins, and certain nutrients.
• Water carries oxygen and nutrients to cells.