Water is the source of life on Earth... You've probably heard this statement many times. Today, let's talk about how much water is in one of the main representatives of this life — the human body.

Since water is an excellent solvent, it can transport numerous substances.

On average, water constitutes approximately 65% of the human body, with 70% of it located inside the cells and 30% in the extracellular space.

The Role of Water in the Human Body

‍Water is present in every part of the complex human organism. To understand why there is so much water, let's first look at its primary functions.

The main task of water is its participation in metabolism. All substances that enter the stomach undergo a series of complex transformations in the digestive system. As a result of this synthesis, proteins are broken down into amino acids, fats into glycerin and fatty acids, and starch into glucose. As you may have guessed, all these processes occur in water.

Another important function is maintaining osmotic pressure inside the cell, essentially ensuring its integrity. Since the cell needs to absorb and excrete substances, it acts as a semi-permeable membrane. If we describe this process using cells as an example, it would look something like this: The pressure formed by the solution inside the cell must equal the pressure outside the cell. When the body is dehydrated or intravenous solutions with too high a salt content are administered, the cells will shrink, releasing water outside. Conversely, if too much pure water or a solution with low osmotic pressure (low salt content) is administered intravenously, the cell will absorb water to equalize the pressure.

The acid-base balance in the human body is also a critical factor regulated by the water environment. For example, saliva, which is a water-based solution, can reach a pH level of 8, while gastric juice has a strongly acidic environment with a pH of 1.5 - 2.

Thermoregulation and heat exchange also occur thanks to water. The principles of thermoregulation involve increasing heat dissipation when body temperature rises and conserving it as much as possible when it drops. These processes can be observed when it's hot outside, meaning external heat is excessive, or during physical exertion when extra energy is released due to the breakdown of sugars. In these cases, a person starts sweating and releasing sweat, i.e., water, to remove excess heat from the body.

The transport function of water is to ensure the delivery of nutrients through the blood and lymph, as well as the removal of waste products such as urine, sweat, and others.

How Does the Water Content in the Human Body Depend on Age?

‍In the infographic below, we show the water content in the human body at different age stages. The older a person is, the lower the water content. For example, a human embryo can contain up to 90% water, an adult about 65%, and elderly people about 40%.

The Percentage of Water in the Human Body

‍These percentages allow us to calculate how many liters of water are in a person's body. For instance, a newborn baby’s body will contain about 3 liters of water, while a middle-aged man’s body will contain 50 - 60 liters.

This is related to the physiological characteristics of tissues. A child's skeleton is elastic, meaning it contains more cartilage tissue, and therefore more water. As a person ages, bones become harder and later brittle, precisely because the water content in them physiologically decreases. Skin aging and the loss of vascular elasticity are also associated with a decrease in the amount of fluid in tissues.

The Percentage of Water in the Human Body

‍Now let's consider where water is predominantly stored in the human body. The majority of fluid (over 90%) is found in the blood. The amount of water is related to the need for blood to be fluid. The brain consists of approximately 75% water, providing the necessary environment for its normal functioning. The liver contains about 79% water, supporting its vital functions. The kidneys, which play a key role in filtering and purifying the body, contain about 82% water. The skin, which is the external covering, contains approximately 64% water, ensuring elasticity and moisture.

Muscles, important for maintaining motor functions, consist of approximately 79% water. Bone tissue, despite having a solid structure, contains about 31% water, providing the necessary balance of strength and flexibility. Water is present inside cells, and its content depends on the type of cells. For example, brain cells can contain up to 85% water, ensuring optimal conditions for their functioning.

The lungs, containing about 9% of all the blood in the body, hold up to 83% water. This is related to their involvement in partial heat exchange when water evaporates from the surface of the alveoli, providing efficient gas exchange. Bone tissue contains the least amount of fluid due to its dense structure, which is necessary to ensure strength.

How Much Water Should You Drink Per Day?‍

The amount of water you need to drink per day can vary depending on factors such as age, gender, physical activity, and climate. For example, physically active people, pregnant women, or those in hot climates may need more water. It's best to determine your individual water needs by listening to your body’s signals and closely monitoring your sense of thirst.

Keep in mind that factors such as diet and other beverages also contribute to the total amount of fluid you consume throughout the day.

How Much Water Should You Drink?

‍It's often said that a person should drink 8 glasses of water per day. But what determines your daily water requirement, and when should you drink it? Previously in the blog, we discussed how much water adults and children should drink, and whether it can be replaced by other beverages.

What is Dehydration?

‍During physical exertion, illness, or increased environmental temperatures, a person may lose more water than usual. Therefore, it’s essential to increase water intake accordingly. If the balance is disrupted, dehydration occurs, leading to a range of negative consequences. Learn more about what dehydration is and how to avoid it.

Resources:‍

  1. Siri, William E. "Body composition from fluid spaces and density: analysis of methods." (1956).
  2. Mitchell, H.H., Hamilton, T.S., Steggerda, F.R., and Bean, H.W., 1945, The chemical composition of the adult human body and its bearing on the biochemistry of growth: Journal of Biological Chemistry, v. 158, issue 3, p. 625-637.
  3. "The Water in You: Water and the Human Body." U.S. Geological Survey. URL:  https://www.usgs.gov/special-topics/water-science-school/science/water-you-water-and-human-body

ÎNTREBĂRI FRECVENTE

How did we learn that the human body is composed of water?

The first knowledge that the human body is made up of water can be traced back to ancient medicine and philosophy. As early as the ancient Greek period, scholars and philosophers like Empedocles and Hippocrates theorized that the body consists of four fundamental elements: fire, air, earth, and water.The widespread information that the human body is 60-70% water primarily comes from modern medical science and research conducted over the years. This knowledge is crucial for maintaining our health and understanding how different aspects of our body interact with water.

How much water is in a person weighing 60 kg?

A person is composed of approximately 60% water by weight. Therefore, for an individual weighing 60 kg, about 36 kg (60% of 60 kg) would be water. Since 1 liter of water has a mass of approximately 1 kg, 36 kg of water is equivalent to about 36 liters. So, by these estimates, a person weighing 60 kg contains roughly 36 liters of water in their body.

How long can a person survive without water?

There is no exact information on how long a person can survive without water, as it greatly depends on specific conditions and individual factors. Typically, the survival period without water is limited to just a few days.

However, there are cases of prolonged survival without water in extreme conditions. For example, in 1979, Maurizio Herzog, an Austrian mountaineer, survived for more than 18 days without food or water after falling into a deep mountain crevice in Peru. However, this was an exceptional case, and such survival in extreme conditions is rare.

In any case, dehydration leads to serious complications and quickly becomes critical for the body. Regular water intake is crucial for maintaining vital functions in the body.

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