Water Distribution in the Body

Water content in the Human Body

Water is a key component in human body. Water is dispensed throughout the whole body including organs and cells. Water content in adult men is around 60% of the body weight. Water content in adult women is around 50-55% of the body weight. For a man that weighs 70 kg, water content is around 42 liters. The average content can vary among individuals due to differences in body composition. While in lean body mass, water content is constant in mammals at 73%, body fat or adipose tissue is only around 10% water. Total body water is influenced by body fat relative mass. This is related to influences of gender, age and aerobic fitness on total body water. Total body water content is lower in older persons and women due to lower fat-free mass. Total body water content is relatively high in athletes.

Water content of Different Organs

Water is distributed throughout the entire body and all organs. Composition of various organs determines their water content. The water content of different organs ranges from eighty three percent in blood to only ten percent in adipose tissues. Water content of organs and tissues by weight is as follows.

Water content of brain is around 75% of the weight. Water content in blood is around 83%. Water content in liver is around 68%. Water content in kidney is around 83 %. Water content in adipose tissue is around 10%. Water content in muscle is around 76 %. Water content in skin is around 72%. Water content in heart is around 79%. Water content in lungs is around 79%. Water content in spleen is around 76 %. Water content in intestine is around 75%. Water content in skeleton is around 22%.

Water Distribution among Body Compartments

Intracellular and extracellular are the two main compartments where water is distributed. The intercellular compartment contains about two thirds of body water. The extracellular compartment contains about one third of body water. The extracellular compartment consists of interstitial fluid and plasma fluid. Interstitial fluid and plasma fluid have similar electrolyte composition with chloride and sodium being the most abundant ions. There are also other compartments that contain water, such as eyeball fluid, lymph and cerebrospinal fluid. These compartments contain small amount of water and typically considered to be part of the interstitial fluid.

Absorption and Distribution of Water in the Body

Gastrointestinal tract absorbs water after ingestion. Water then gets into the vascular system and interstitial spaces respectively. Water eventually gets transported to every cell. Intracellular water accounts for about 65% of total body water.

After passing through stomach, water gets absorbed mostly in the early segments of small intestine including the jejunum and the duodenum. Small amount of water gets absorbed in the stomach and the colon. The colon absorbs 1.3 liter a day and the small intestine absorbs 6.5 liter a day. This amount of water is related to how much water is ingested daily and how much water is produced by secretions from liver, pancreas, stomach, salivary glands and the small intestine itself. Water absorption process is very rapid. According a study, after ingestion, it takes only about five minutes for water to appear in blood cells and plasma.

Water gets into plasma from intestinal lumen by passive transport, which gets regulated by osmotic gradients. Blood circulation then transports water molecules for distribution throughout the entire body, to the cells and to the interstitial fluids. In the interstitial compartment, water moves freely. The aquaporin or water specific channels help water move across cell membranes. Osmotic and hydrostatic pressure regulate fluid exchanges between compartments. Changes in the extracellular fluid osmolality regulates water flows.

The body keeps losing water. The water pool in the body gets renewed by ingestion of water. How fast water pool gets renewed depends on how much and how frequently water is ingested. For a person drinking two liters of water a day, water molecule stays in the body for about 10 days. In about 50 days, 99% of the body water gets renewed. Renewal of the body water pool helps maintain balance of body water.

Amazing is how water is distributed in the body and how it plays vital role in keeping the body functional.


What is Intracellular Water?

Human body is made up of mostly water. 45%-65% of body weight can come from total body water. Amount of total body water can vary depending on gender, age and fitness level. Body water is not just in our blood but also in our muscles, fat, organs and inside every cell. Our body water is divided into two basic groups including intracellular water (ICW) and extracellular water (ECW).

Intracellular Water

Cells in our body contain water, which is known as intracellular water. Intracellular water comprises 70% of the cytosol, which is a combination of water and dissolved elements. In healthy people, intracellular water amounts to two third of the water in the body.

The intracellular water is where important cellular processes take place. It has many functions. A very important one helps molecules get transported to the different organelles inside the cell. The intracellular water begins a job where it is discontinued by extracellular water. The intracellular water continues the pathway for fuel to be transported to the cells.

Balance for Water

It is important to have balance in the amount of ICW and ECW. Water distribution in a healthy body water has been estimated at a 3:2 ratio of ICW: ECW. The ratio between ICW and ECW should remain at same levels with respect to each other. When body water gets out of balance, it can cause changes in your body composition and health. Whether such changes are negative or positive depends on what type of water gets out of balance.  

Increased ICW

It is not necessarily a bad thing to have slightly more ICW. It can actually signal healthy changes. Muscle mass increases when size and number of muscle cells are enlarged. Enlarged muscle cells require or are able to take in more ICW in order to power their cellular functions. Research suggests that exercise can result in increase in ICW in humans. Increase in ICW because of exercise is a sign of increase in lean body mass, which has health benefits. Following are some of such health benefits.

Increase in Energy Use

Basal Metabolic Rate (BMR) is the amount of calories that a human body burns at rest. It is about the amount of calories that body needs to operate and maintain its daily functions. Increase in lean body mass will cause BMR to rise, which in turn, will burn more calories and help create calorie deficit. Calorie deficit is good for losing fat.

Increase in Strength

Lean body mass is also known as fat free mass. Lean body mass is about the weight due to muscle mass, water, bone and protein. Lean body mass can increase due to increase in muscle mass. Typically, increase in muscle mass means increase in strength.

Enhanced Immune System

Increase in lean body mass achieved through exercise has been linked with enhanced immune system functionality. This can make it easy for your body to combat illness.

Diagnosing level of ICW    

It is important to know how to determine body water level including ICW. It can help balance levels of both ICW and ECW. There are multiple methods to determine body water level. Bioelectrical impedance analysis (BIA) method is the one that can determine not just total body water but also level of ICW.

BIA method is practical for those that do not have serious medical issues. In this method, a small electrical current is applied to the body. The current experiences opposition or impedance, which gets measured. This impedance result helps BIA device to produce report on total body water. Advanced BIA devices can also reveal the level of both ICW and ECW.

Maintaining right level of ICW

Maintaining or slightly increasing level of ICW if necessary is possible by means of increasing lean body mass or muscle mass through exercise. Increase in number and size of muscle cells require more water to maintain their functions. Exercising is also helpful in combating obesity. Consultation with a doctor and developing healthy lifestyle can help maintain healthy level of ICW.


What is Extracellular Water?

We are made up of mostly water. 45-65% of our body weight is due to total body water. Amount of water in human body can vary depending on gender, age and fitness level. Total body water is divided into two basic groups. One is intracellular water (ICW) and the other one is extracellular water (ECW).

Extracellular Water

The water in the body that is located outside your cells is categorized as extracellular water. This category includes the water in your blood. About one third of the body water is attributed to ECW. ECW is in transcellular fluid, interstitial fluid and blood plasma. ECW is of great importance as it facilitates control of the movement of electrolytes and oxygen delivery to the cells. It also helps clear waste from metabolic processes.

Need for Balance

The ratio between ICW and ECW should be 3:2 in a healthy body. It is important that you’re ICW: ECW remains at the healthy level with respect to each other. When your body water gets out of balance, changes can occur in your body composition and health. Whether such changes are positive or negative depends on the type of water that gets out of balance.

Excess ECW

Increase in ECW in relation to your ICW is not a good thing to happen. It can be responsible for various health issues. Swelling in your limbs and excess weight can be caused by increased ECW. Increased ECW can cause other kinds of imbalances in the body. Such imbalances may be related to sodium, protein, hormone, magnesium, potassium and ph. Because of such imbalances, you can develop decreased mental alertness, hypertension, dizziness, nausea, headaches, shortness of breath and fatigue. Excess ECW is linked with numerous health risks, some of which are as follows:


In case of inflammation, the damaged area in the body gets some additional blood flow. This causes ECW to increase in a particular area. When a part of the body gets bruised or damaged, inflammation occurs. It is a bodily response to injury and linked with temporary increase in ECW.  

Chronic inflammation is not always readily detected and is more serious. It has caused by cellular stress and dysfunction and marked by long-term swelling or increased ECW. When chronic inflammation is allowed to persist, it can result in serious diseases including cancer, renal failure and heart disease.

Renal Disease (Kidney Failure)

Kidneys filter body water and remove toxins produce in the body. Sodium is one of the important substances that kidneys filter out. Sodium is found in salt. When your diet has more sodium than kidneys can filter out, which happens in people with failing kidneys, your level of ECW will increase. The increased ECW is shown in some cases in visible swelling throughout the body, which is a condition known as edema. Edema can put additional stress on the body by contributing to blood pressure, weight gain and other complications.

Unhealthy level of Fat (Obesity)

Obese people typically have too much fat mass, which has various negative effects including body water disruption due to excess ECW. This happens as excess visceral fat can trigger production hormones that can result in the disruption of a bodily system called RAAS. The excess ECW causes stress in the body by affecting the internal organs, which can worsen obesity and cause a dangerous cyclic effect.

Determining Balance

It is important to know body water level including ECW. Two of the major methods that help determine your body water content, include BIA method and dilution method.

Dilution Method

In dilution method, a known dose of heavy water (deuterium oxide) gets ingested in the human body. The heavy water gets allowed to get distributed in the body. Once the heavy water is done settling in the body, the amount of heavy water is compared with the amount of normal water. The proportion then helps determine the amount of total body water. In order to determine level of ECW, sodium bromide is used instead of heavy water.

The dilution method is considered to be a gold standard for determining total body water. The test needs to be done by a trained physician at a hospital. It takes several hours to complete the test. During the test, any fluid that is going in or out of the body needs to be carefully recorded.

Doctors perform such test only when there is a serious health complication and need to know total body water level with absolute certainty.

BIA Method

The other method is BIA method. This method is practical for those that do not have serious medical issues. In BIA method, a small electrical current needs to be applied to the body. The current experiences opposition or impedance, which is measured. Based on the impedance result, the BIA device can report total body water level. It takes advanced BIA device to determine levels of ECW and ICW. This can reveal ratio between and status of balance or imbalance of ICW: ECW.

Maintaining Balance

The balanced ratio between ICW and ECW is 3:2, which is ideal for optimal health. We should try to maintain the balanced ratio so that ECW does not get out of balance. Avoiding excess ECW is particularly important. Exercising regularly and a healthy diet can be helpful in preventing increase in ECW.

Lowering the amount of salt or sodium in your diet can help reduce excess ECW. When excess sodium is consumed, the body tends to draw water out of cells at the expense of ICW. Lowering sodium intake has many positive health benefits including reduction of high ECW.

It is obviously important to know the body water level including ECW and keep them in balance. A healthy lifestyle can keep ECW in balance naturally. Getting help from a doctor is highly useful in keeping ECW level in check.

Last update: October 22, 2017 03:59:42 pm

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