Body Composition: The Importance of Body Water

Body composition is a way of describing specific parts of the body. This involves fat, protein, minerals, and body water percentage concerning the total body mass. The well-known BMI test is an auxiliary method for measuring body composition and though it is easily accepted by most people. Body composition is considered to be an indicator of physical fitness related to health. It can be used to monitor nutritional status, body fluid balance, body fat percentage, and evaluate growth and development. Knowing body composition always helps verify services such as personal training, patient care,  nutritional supplement, and special group health.

What is Body Water Percentage?

The total mass of the human body which is comprised of water is known as body water percentage. It accounts for about 60-70% of the total body weight in the human body. For example, it accounts for about 75-80% of the water in newborns, about 60% in adult men, and about 45-60% in adult women. (2)

The total body water content (TBW) is the sum of all the tissues, blood, bones, and various fluid components in your body. The weight and volume of the body’s total water content are important indicators of the body.

Why does it matter?

Because more than half of the body weight in humans is composed of water, it is quite evident that water is a necessity for the human body to function properly.

Water in the human body is mainly used to help the human body to function normally, such as forming blood and plasma, forming digestive juice, helping nutrient absorption, oxygen transportation, regulating body temperature, excreting waste, participating in body metabolism, and maintaining cardiovascular system circulation.

The Relationship between Water Weight and Body Composition:

The variations in the body water weight are the main cause of weight fluctuations. Water comprises more than half of the body weight in humans, which means that even small changes in the water composition can have considerable effects on the total body weight and body composition.  The moisture in the urinary system, the feces in the intestines, and the moisture in other parts of the body can fluctuate greatly within 24 hours.

What is the Ideal Body Water Percentage?

Body Water Percentage Chart:


12-18 Years

19-50 Years

51 and older


52-66% of body weight

43-73% of body weight

47-67% of body weight


49-63% of body weight

41-60% of body weight

39-57% of body weight


Calculating the water needs for the human body:

Drinking plenty of water is a healthcare remedy that we firmly believe in. The benefits brought by water intake are innumerable; it not only meets our body’s needs but is also the most natural and effective skincare product. However, despite everyone understanding the importance of water to the human body, not everyone knows how much water should be consumed in a day.

Generally speaking, drinking 8 glasses of water a day is generally recognized by the general public. However, if you want to know your body’s daily water needs more accurately, you can calculate it according to this formula:

Age less than 30 years old: weight (kg) × 40 = water volume required per day (ml)

Age between 30 and 55 years old: weight (kg) × 35 = water required per day (ml)

Age over 55 years old: weight (kg) × 30 = water required per day (ml)

This calculated value can be used as a reference for your daily drinking water, but this does not mean that it is universally applied to the four seasons of the year. To be honest, there is no absolute fixed value for the daily water demand per person. It will vary according to various factors such as living environment, diet and rest; for example, when we are in a high-temperature environment, the amount of water required That is, there will be a lot of lower temperature environments. (4)

How to calculate body water percentage?

The water content can be determined using various methods. However, some of these procedures can only be performed clinically or by doctors. The easiest way to determine the water content is to take measurements with body composition scales. These body composition scales usually work with bioelectrical impedance analysis. For this purpose, a weak current is passed through the body and the water content is measured via the body resistance. This measuring method is not 100% exact but is completely sufficient for a good assessment and for recognizing meaningful trends.

How is body water measured?

There are different methods to measure the total body water content. Some of these methods are explained below:

Fluid Balance:

The balance between drawn and excreted or discharged amounts of liquid from the body is known as the fluid balance. It is created by measuring and documenting the import and export of liquids in a certain time interval, for example, in 24 hours.

The human body can absorb an average of 2,000 to 2,400 ml of water in one day. Approximately, 1,000-1,500 ml/day are absorbed through drinks, and approx. 700 to 900 ml/day through water contained in solid food. In addition, mitochondrial oxidation produces around 200-300 ml of oxidation water per day. The exact fluid requirement – like the fluid loss – depends on many factors, including age, physical activity, and the ambient temperature.

The amount of water absorbed or formed is lost again in various ways, mainly through the urine (1,000-1,500 ml /day), but in smaller amounts also through the stool (150-200 ml/day). The insensitivity perspective, i.e., the unnoticed loss of water through the skin, mucous membranes, and breathing, results in a deficit of 800 ml/day.

Having an idea of the total water absorbed by the body and the total amount of fluid secreted, we can easily calculate the total body water content in a person. (5)


Another method of measuring the total body water content is through measuring the deuterium or tritium water dilution method. This method is complex, and can only be carried out by skilled professionals because sophisticated machinery such as mass spectrometer is needed in this method.

The total body water can be determined with the help of mass spectrometry from the deuterium or tritium content of the expired breath. For this purpose, the test person is given a known dose of deuterium (D2O) or tritium water (T2O). After 3-6 hours, the marked water is evenly distributed in the body. The isotope dilution in the body water can then be determined from the isotope content of the water in the air we breathe, and thus the amount of water itself can be calculated. (6)

Bioelectrical Impedance Analysis:

Bioelectrical impedance analysis is a device designed to estimate body composition based on the different conductive properties of different body tissues.

This technology is easy to use and does not require special skills and training. Many gyms use this method to determine body composition. Many smart scales have also entered the home. However, different types of electronic scales and the number of electrode pads will still affect the measurement. Value and the result are related to the amount of water in the body. (7)

What is Extracellular Water and Intracellular Water:

Extracellular Water

The 40% of the total body water that makes up extracellular water is made up of around 30% of interstitial fluid, around 7% of the intravascular fluid. the plasma volume, and around 3% of the transcellular fluid.

The extracellular volume cannot be measured exactly, but it can be estimated relatively accurately. Substances such as inulin or radioactive sodium can leave the vessels and do not distribute themselves within the cells, but unfortunately also do not distribute exclusively in the entire extracellular space.

Intracellular Water

About 60% of the total body water content is contained in the intracellular compartments of the body. This is because water is readily available to the vital metabolic reactions occurring inside the cells, and for this purpose, a large amount of water is retained in the intracellular compartments.

Although the majority of body water is in the intracellular space, this proportion must not increase significantly. A rise in intracellular fluid means for a cell surrounded by a membrane that it swells and, if nothing is done about the increasing water mass, it ultimately means cell death.

Extracellular Water/ Total Body Water Analysis:

The extracellular water ratio is the ratio of extracellular water to total body water and is an important indicator of whether the body’s water is balanced. If the body is healthy, the extracellular water ratio should be kept in the range of 0.36 to 0.39. If the extracellular water ratio exceeds this range, please consult your doctor. (8)

Using bioelectrical impedance vector analysis, the liquid state in the patient’s body can be graphically represented. If the proportion of extracellular water is particularly high, this may be an indication of water retention in the patient’s body.

What is a healthy water balance?

To maintain good health, the body needs an appropriate amount of water. Too much or too little water can cause serious problems. The water in the body contains electrolytes. Electrolytes are minerals such as sodium and potassium, which can help achieve many important body functions. The body needs various electrolytes to maintain proper balance.

We lose water through urination, defecation, breathing, skin evaporation, or sweating. Among them, urination is the most important way. There is a water balance regulation system in the human body, which ensures a dynamic balance between fluid intake and loss. When the body has insufficient fluids, the “thirst center” in the brain is stimulated to produce a sense of thirst and trigger drinking behavior.

If the body lacks more than 1% of body weight and is not supplemented in time, some symptoms will occur. If you have symptoms such as joint pain, muscle pain, constipation, and a strong urine smell and yellow color, it means that your body is already in a state of dehydration.

When the water intake exceeds the capacity of the kidney to excrete, it can cause excessive water in the body or water intoxication, and water intoxication can lead to hyponatremia. Normal people rarely suffer from water intoxication. Those who suffer from kidney, liver disease, and congestive heart failure are prone to water intoxication in high-temperature environments.

What does Increased Intracellular Water Mean?

If you come to know that your intracellular water levels have been increased, this is not essentially bad news for you. The increase in the intracellular water levels means that your body composition is changing for the better. Increased intracellular water signals increased body energy and strength, according to a research paper published in PubMed. This means that maintaining your hydration levels at optimal can help you boost your immunity and body composition greatly.

What does Excess Extracellular Water Mean?

Contrary to increased intracellular water levels, the increase in extracellular water levels signals some kind of pathological process going on in the body. An increase in the volume of the extracellular compartment, in particular the interstitial sector, results in generalized edema due to the inflammatory processes occurring in the body. Increased extracellular water can also signal other sinister pathologies such as renal disease, as the diseased kidneys can not get rid of extra water from the extracellular compartments. (9)

Benefits of Drinking Water:

Although it is not a special drink, water is the basic necessity of life. Almost every metabolic reaction occurring in the body requires water in some of its pathways. Water acts as the solvent for the majority of the compounds in the human body, and it is also the fluid responsible for maintaining the thermostatic balance in extreme temperatures. Maintaining your hydration at an optimum will not only help you gain strength but will also make you more focused on daily life tasks.

Recommended Daily Intake of Water

The recommended daily intake of water can be precisely calculated according to the age and weight of a particular person by using the formulas given above. However, as a rule of thumb, experts recommend drinking at least 8 glasses of water every day for an adult. Regular hydration is therefore essential for the functioning of the body.


  1. What Is Body Composition?. WebMD. (2021). Retrieved 5 November 2021.
  2. Understanding body water percentage – Health insights | Withings. (2021). Retrieved 5 November 2021.
  3. Body Water Percentage: Average, Ideal, How to Maintain and Determine. Healthline. (2021). Retrieved 5 November 2021.
  4. Roumelioti, M., Glew, R., Khitan, Z., Rondon-Berrios, H., Argyropoulos, C., & Malhotra, D. et al. (2018). Fluid balance concepts in medicine: Principles and practice. World Journal Of Nephrology7(1), 1-28.
  5. Van Marken Lichtenbelt, W., Westerterp, K., & Wouters, L. (1994). Deuterium dilution as a method for determining total body water: effect of test protocol and sampling time. British Journal Of Nutrition72(4), 491-497.
  6. Bio-Electrical Impedance Analysis (BIA) – Body Mass Analysis. (2021). Retrieved 5 November 2021.
  7. Inner Image | Interpreting Your Results. (2021). Retrieved 5 November 2021.
  8. Body Water: Percentage and Ratios You Should Know – InBody USA. InBody USA. (2021). Retrieved 5 November 2021.

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