How Much Water Is in the Human Body?

Water in the Human Body
Water serves several functions in the human body. Babies have the highest percentage of water, followed by children, men, and women. Women have a lower percentage because they typically have more body fat than men.

Have you ever wondered how much water is in the human body? The average amount of water ranges from 45-75%, but it varies according to age, gender, and health. Here’s a look at how much water is inside a person.

The average human is about 60% water. This is approximately 45 kg (100 lb) of water for the average adult.

Amount of Water in the Body

Babies and children contain the highest percentage of water. A newborn averages about 74% water (64% to 84%), while a 12-year-old averages about 60% water (49% to 75%). The average adult male is about 60% water, while the average adult female is 55% water. Women naturally have more fatty tissue than men, resulting in a lower percentage of water. An overweight person has a lower percentage of body water than a lean person. Elderly people may have slightly less water than when they were younger because they are more susceptible to dehydration. The average male over age 51 is about 56% water, while the average female of the same age is about 47% water. Feeling thirsty means you’ve already lost 2-3% of your body’s water.

Average Percent WaterAverage Weight (U.S.)Water Weight (kg)Water Weight (lbs)
Newborn74%3.5 kg (7.5 lb)2.6 kg5.5 lb
12 year old child60%41.5 kg (91.5 lb)24.9 kg54.9 lb
Adult male60% (range: 43-73%)76.4 kg (168.4 lb)45.8 kg101.0 lb
Adult female55% (range: 41-60%)88.8 kg (195.8 lb)48.8 kg107.7 lb
51 year old male56%88.3 kg (194.7 lb)49.4 kg109.0 lb
51 year old female47%75.5 kg (166.5 lb)35.5 kg78.3 lb
Average amount of water in the human body. Values depend on age, gender, fitness, and hydration levels.

Where Is Water in the Body?

About two-thirds of the body’s water is inside cells (intracellular fluid), while one-third is outside of cells (extracellular fluid). About 20% of the body’s water is in blood plasma.

The amount of water varies in different organs. As you might expect, bones contain a relatively low amount of water (31%). The skin is 64% water. The muscles and kidneys are 70% water. The human brain and heart are each 73% water. The lungs are the organ with the highest percentage of water (79%).

Functions of Water in the Human Body

Water is essential for life because it serves so many functions. Here are some of the body’s uses of water:

  • Water is the primary building block of cells.
  • It’s also a building block of important molecules, such as hormones and neurotransmitters.
  • 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 keeps membranes moist. It helps keep the eyes clean and hydrated, is essential for the senses of smell and taste, makes it possible to swallow food and excrete feces.
  • 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 flushes waste and toxins from the body via urine and perspiration.
  • Water is the principal solvent in the body. It dissolves minerals, soluble vitamins, and certain nutrients.
  • Water carries oxygen and nutrients to cells.