What Percentage of the Human Body is Water?
The percentage (total amount of water content) in the body by mass can range from 78% in infants to as little as 45% in the elderly.
Total body water (TBW) is made up of the percentages of water present in the body’s various fluid compartments. According to Boron’s Textbook of Medical Physiology, water in the human body is found in what are referred to as intracellular and extracellular fluid compartments.
The intracellular fluid compartment refers to the total space inside cells. Two-thirds of the body’s total water is found here. The extracellular fluid compartment refers to both the space between cells (referred to as “interstitial” fluid) and to blood plasma. Combined, these contain one-third of the total water in the body.
Knowing about these compartments is important because age, sex, nutritional status, and body composition-dependent shifts in the fluid content of the intracellular and extracellular fluid compartments are what produce variability in the percentage of total body water throughout one’s life.
Variations in diet found in different countries make it more likely for countries with higher obesity rates to see lower average total body water. This is because fat has a lower percentage of water than muscle.
The typical percentage of the human body that is water is 60% in adult men according to Dr. Jeffrey Utz of Allegheny University and 50% in adult women according to the US National Academy of Sciences.
Table of Contents
- Which Organs In The Human Body Have A Higher Percentage Of Water?
- Which Organs In The Human Body Have A Lower Percentage Of Water?
- What Is The Water Percentage In The Female Body?
- What Is The Water Percentage In The Male Body?
- What Is The Water Percentage In A Child's Body?
- How Is The Water Percentage In Animal Bodies Different From The Human Body?
- How Does Water Help Body Functions?
Which Organs In The Human Body Have A Higher Percentage Of Water?
The organs in the human body with the highest percentages of water are the brain (80-85%), kidneys (80-85%), heart (75-80%), lungs (75-80%), liver (70-75%), muscles (70-75%), and skin (70-75%). The brain and kidneys are the organs with the highest percentage of water according to the Canadian BCcampus Human Anatomy and Physiology textbook. The percentage of water in these organs is outlined in this graphic.
The reason different organs in the human body have different percentages of water is their different functions. Because two-thirds of total body water is contained inside cells, organs that are large and highly cellular contain a higher percentage of total body water.
Which Organs In The Human Body Have A Lower Percentage Of Water?
The organs with the lowest percentage of water in the human body are the teeth (8%) and bones (20-25%) according to the Human Anatomy and Physiology textbook.
This is explained partly by the fact that teeth and bone are primarily composed of mineralized hydroxyapatite crystals which do not contain water.
While not an organ, blood is approximately 50% water.
What Is The Water Percentage In The Female Body?
The water percentage in the female body ranges from 41% to 61% and averages 50% by weight according to a 2005 study by the US National Academy of Sciences entitled Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. The 50% average is equal to approximately 31 liters or 8 gallons for a 70kg/154lb female.
The lower percentage of total body water in females versus men is accounted for by their greater percentage of body fat and a lower percentage of muscle mass. This is relevant because adipocytes (fat cells) hold much less water than myocytes (muscle cells).
What Is The Water Percentage In The Male Body?
The water percentage in the male body has a wider range than women at 43% to 73%, with a higher average of 59% according to the 2005 US National Academy of Sciences study. The 59% average is equal to approximately 42 liters or 11 gallons for a 70kg/154lb male. The higher percentage of total body water in males versus women is explained by their higher percentage of muscle mass, which has higher water content than fat cells.
What Is The Water Percentage In A Child's Body?
The water percentage in a child’s body ranges from 60% to 75% in the first year of life and falls slowly to adult levels by puberty. In infants and children, the total body water percentage is higher due to there being more water in the extracellular compartment.
According to the Nelson Textbook of Pediatrics, at birth, an infant’s total body water is approximately 75% of their weight. However, as extracellular fluid volume decreases and body fat increases during the first year of life, total body water percentage will decrease to 65% at 6 months and 60% at 1 year. Total body water percentage will continue to decrease until puberty when adult values will finally be reached.
How Is The Water Percentage In Animal Bodies Different From The Human Body?
The water percentage in animal bodies tends to be higher than the human body, though with some notable exceptions. Biopsychologist Israel Ramirez of the Monell Chemical Senses Center in Philadelphia says this is because humans have a higher percentage of body fat than animals, with fat containing less water than muscles and organs. Another factor may be that the water in the digestive tract makes up an appreciable percentage of total body water in several mammalian species, but not humans.
Most animals tend to have a Total Body Water (TBW) percentage in the low- to upper-70% range, with some clear outliers:
- Mammals. One study published in the American Journal of Clinical Nutrition reported mean values for the percentage of total body water for the majority of species ranged between 70% and 76%. A century-old survey in 1921 by C.R. Moulton of the Institute of American Meat Packers found percentages for mature animals of around 71% for dogs and cats, 74% for pigs, 76% for mice, and 73% for rats and rabbits.
- Fish. Another nearly century-old study from the Zoological Laboratory of the University of Wisconsin in 1925 took samples of perch and trout. They found that most had a body water percentage in the mid- to upper-70% range. At an even further extreme, and admittedly not actually in the fish category, a 1942 study in the journal Nature found a Jellyfish was 95.6% water.
- Reptiles. A 1999 study by Michael J. Angilletta Jr. in the journal Copeia of the American Society of Ichthyologists and Herpetologists, measured the water in 37 lizards in South Carolina and found most were fairly close to the average of 72%. However, when it comes to snakes, a 2003 study by Stephen M Secor of the Depart of Biology at the University of Mississippi found 20 diamondback water snakes averaged only 65% body water by mass.
- Birds. A 1984 study in the journal The Condor of The Cooper Ornithological Society stated that adult birds of virtually all sizes have total body water of about 60%. They point out that while young birds are up to 80% water, this decreases with age and would make it difficult to fly. Stripping out some outlier results which they doubted the methodology of, their survey of 22 different species of marine and aquatic birds found mean percentages ranging from 57% to 68%.
How Does Water Help Body Functions?
Water helps body functions by acting as a vital nutrient supporting numerous critical roles including as a building material, solvent, participant in enzymatic reactions, transporter of nutrients and wastes, thermoregulator, lubricant, and in maintaining vascular volume. A study published in the European Journal of Clinical Nutrition detailed these roles as follows:
- Building material: Water is present inside every one of our cells.
- Solvent: Water allows various ionic compounds such as electrolytes, amino acids, and glucose to dissolve in it.
- Enzymatic reactions: Water participates in numerous enzymatic reactions. For example, the process called hydrolysis which involves using H₂O to break apart protein, carbohydrate, and lipid macronutrients into their amino acid constituents which are better used by our bodies.
- Transporter: Water functions as a transporter that allows for the maintenance of cellular homeostasis by transporting nutrients to cells and removing excess waste from them. And it allows various transport systems to function, allowing for the exchange of gasses and nutrients, which is essential for the proper functioning of all body systems.
- Maintaining vascular volume: Water in the form of plasma allows red blood cells to circulate throughout the body. All body systems require water for adequate hydration and oxygenation.
- Thermoregulation: Water allows for body heat loss through sweating.
- Lubricant: Water in combination with other viscous compounds acts as a lubricant for joints as well as for gastrointestinal, respiratory, and genitourinary tracts.
Because of these roles, a decrease in total body water content, such as in various states of dehydration, can negatively impact the body’s proper functioning and homeostasis.
How Much Of Your Body Weight Is Water?
Adults Have 50-59% of their body weight as water on average. In females, due to a higher body fat content and lower muscle mass, total body water content by mass is lower, averaging 50%. For a 70kg/154lb female, this is approximately 31 liters or 8 gallons of total body water. Of which 60% or 21 liters is located in the intracellular fluid compartment and 40% or 14 liters in the extracellular fluid compartment for female humans.
In male humans, due to lower body fat content and higher muscle mass, total body water content by mass is higher, averaging 60%. For a 70kg/154lb male, this is equal to approximately 42 liters or 11 gallons of total body water. Of which 60% or 25 liters is located in the intracellular fluid compartment and 40% or 17 liters is located in the extracellular fluid compartment.
It is important to remember that as humans age, they experience changes in their total fat and muscle content, as well as changes to their extracellular fluid volumes. This introduces variability in the water content of the body and its relationship to one’s weight, with the percentage of total body water generally decreasing with age. The chart below displays the fluctuation in body fat percentage in males and females of various age ranges.
Does Drinking Water Help For Weight Loss?
Yes, drinking water does appear to help weight loss. However, the exact mechanism is not fully known.
An article published in the journal Obesity assessed the effects of increased water intake in conjunction with a hypocaloric diet (a very low-calorie intake diet) on weight loss in middle-aged and older adults. It found that water consumption prior to daily meals led to a roughly 2kg increase in weight loss over 12 weeks as compared to a hypocaloric diet alone.
They ascribed this ability to the fact that consuming water with meals reduces sensations of hunger and increases the sensation of fullness which both cause an acute reduction in the amount of caloric intake during each meal.
Additionally, they surmise that increased consumption of water substitutes the consumption of energy-containing beverages in the diet, which can further reduce weight.
Their findings are corroborated by several other studies, including a study entitled “Drinking water is associated with weight loss in overweight dieting women independent of diet and activity” by Dr. Jodi Stookey of the Children’s Hospital Oakland Research Institute in the United States. The study found that an increase in water consumption (greater than or equal to 1 liter/day) when combined with a hypocaloric diet was associated with an average 2.3 kg (5 lb) decrease in body weight. This change was paralleled by a decrease in both waist circumference and percent body fat.
The concept of how water consumption can promote weight loss as one of the benefits of drinking water is discussed further by dietitian Joe Leech MSc in the video below.
What Is The Optimum Percentage Of Water In The Body?
There is no scientifically established optimum percentage of water in the body, though the average is 50% for adult men, 59% for adult women, 75% for infants at birth, 56% for elderly males, and 47% for elderly females.
The amount of water in the body in the short term varies based on the balance between intake and loss. The human body obtains water primarily by absorbing dietary H₂O from the digestive tract and by producing minute amounts of H₂O during the metabolism of nutrients. While the loss of body water is accomplished primarily by urinary excretion, evaporation during sweating, respiration, and defecation.
It is this give-and-take process of various complex mechanisms that allows the human body to maintain a balanced percentage of water in the body, as illustrated in these calculations from a 2010 paper from the University of Lausanne in Switzerland.
Water from beverages 1.5 L
Urine 1.5 L
Water from food 0.7 L
Sweating 0.45 L
Water from metabolic reactions 0.3L
Respiration 0.35 L
Total water input 2.5 L/day
Feces 0.2 L
Total water output 2.5 L/day
To answer the question of what the optimum percentage of water in someone’s body is quite difficult as it varies based on one’s age, sex, nutritional status, environment, and even level of activity.
Instead, it is better to concern ourselves with making sure that we are adequately hydrated so our physiologic mechanisms can maintain the optimum water percentage necessary for our bodies. Healthy adults should drink at least 1½ to 2 quarts (approximately 2 liters) of fluids a day. Under normal circumstances drinking more is usually better than drinking less, because excreting excess water is much easier for the body than conserving water.
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