How many gallons of water in the human body

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.

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.

References

• Adan, Ana (2015). “Cognitive Performance and Dehydration.” Journal of the American College of Nutrition. 33(2): 71-78. doi:10.1080/07315724.2012.10720011
• Jéquier, E., Constant, F. (2010). “Water as an essential nutrient: the physiological basis of hydration.” European Journal of Clinical Nutrition. 64: 115-123. doi:10.1038/ejcn.2009.111 
• Mitchell, H. H., et a. (1945). “The Chemical Composition of the Adult Human Body and its Bearing on the Biochemistry of Growth.” Journal of Biological Chemistry. 158: 625-637. 
• Nyman, Jeffry S., et al. (2006). “The influence of water removal on the strength and toughness of cortical bone.” Journal of Biomechanics. 29(5): 931-938. doi:10.1016/j.jbiomech.2005.01.012
• Ohashi, Yashushi, et al. (2018). “Dry weight targeting: The art and science of conventional hemodialysis.” Seminars in Dialysis. 31(6): 551-556. doi:10.1111/sdi.12721
• “The Water in You: Water and the Human Body.” U.S. Geological Survey.
• Tobias, Abraham; Mohiuddin, Shamim S (2019). “Physiology, Water Balance.” In: StatPearls. Treasure Island (FL): StatPearls Publishing.