Category Archives: Water


Magnesium Bicarbonate Water as a Bioavailable Source of Magnesium

Magnesium’s Role in the Body

Magnesium plays a major role in disease prevention and overall health and has numerous functions in the body.  Magnesium is the fourth most abundant mineral and the second most abundant intracellular divalent cation and has been recognized as a cofactor for over 300 metabolic reactions in the body. Some of the processes in which magnesium is a cofactor include, but are not limited to:  1

  • blood pressure
  • cardiac excitability
  • cellular energy production and storage
  • DNA and RNA synthesis
  • glucose and insulin metabolism
  • muscular contraction
  • nerve transmission
  • neuromuscular conduction
  • protein synthesis
  • reproduction
  • stabilizing mitochondrial membranes
  • vasomotor tone

The dietary recommendation (Recommended Dietary Allowances/RDA) for magnesium is:

  • Adult men        400 to 420 mg daily
  • Adult women   310 to 320 mg daily
Table 1. Recommended Dietary Allowance (RDA) for Magnesium
Life Stage Age Males (mg/day) Females (mg/day)
Infants 0-6 months 30 (AI) 30 (AI)
Infants 7-12 months 75 (AI) 75 (AI)
Children 1-3 years 80 80
Children 4-8 years 130 130
Children 9-13 years 240 240
Adolescents 14-18 years 410 360
Adults 19-30 years 400 310
Adults 31 years and older 420 320
Pregnancy 18 years and younger 400
Pregnancy 19-30 years 350
Pregnancy 31 years and older 360
Breast-feeding 18 years and younger 360
Breast-feeding 19-30 years 310
Breast-feeding 31 years and older 320

Source: LINUS PAULING INSTITUTE Micronutrient Information Center 

In the U.S., consumption of magnesium is far below the RDA.  A study conducted in 2012 indicated that forty-eight percent (48%) of the U.S. population consumed less than the required amount of magnesium from food in 2005-2006, and the figure was down from 56% in 2001-2002. They also found that over 30 years, surveys indicate rising calcium-to-magnesium food-intake ratios among adults and the elderly in the United States, excluding intake from supplements, which favor calcium over magnesium.  2 

A magnesium deficit is often associated with the aging process.  The total body magnesium and total magnesium in the intracellular compartment tend to decrease with age. 

One way to determine if you have a magnesium deficit is to take the blood test called RBC magnesium.  This test is used to evaluate magnesium levels in red blood cells and is the most precise way to assess intracellular magnesium status.

Magnesium Deficit is Associated with Disease

Chronic magnesium deficits have been linked to an increased risk of numerous preclinical and clinical outcomes, including:  3

  • alterations in lipid metabolism
  • asthma
  • atherosclerosis
  • cardiac arrhythmias
  • cardiovascular mortality
  • chronic fatigue
  • depression
  • endothelial dysfunction
  • glucose intolerance
  • hypertension
  • inflammation
  • insulin resistance
  • ischemic heart disease
  • neuropsychiatric disorders
  • oxidative stress
  • platelet aggregation/thrombosis
  • stroke
  • type 2 diabetes mellitus
  • vascular remodeling

Magnesium’s role in cardiovascular health is critical.  Dietary magnesium intake has been shown to be inversely associated with mortality risk in individuals at high risk of cardiovascular disease.  4 


Figure 1: Role of magnesium and calcium in the pathophysiology of hypertension, diabetes mellitus, and atherosclerosis.  (Source:  Magnesium and Vascular Changes in Hypertension)

Magnesium Bicarbonate as a Bioavailable Form of Magnesium Supplementation

There are many forms of supplemental and non-supplemental magnesium.  One form that is easy to consume and is considered bioavailable is magnesium bicarbonate.  Short term regular ingestion of magnesium bicarbonate supplemented water provides a source of orally available magnesium.  5  

Magnesium bicarbonate exists only in aqueous solution, so it can never be available in pill/capsule form.

Magnesium bicarbonate (Mg(HCO3)2) is the bicarbonate salt of magnesium. It is formed through the reaction of carbonic acid and magnesium hydroxide.

The chemical formula for magnesium bicarbonate is: 

Mg(OH)2 + 2 CO2 → Mg(HCO3)2

If magnesium bicarbonate is dried, the result will be magnesium carbonate.  Magnesium carbonate can be found as a supplement in powdered form. 

Magnesium bicarbonate can be made at home with just two ingredients:

  • Seltzer water (club soda)  (Carbonic acid)
  • Milk of Magnesia  (Magnesium hydroxide)

Following is the recipe for magnesium bicarbonate:

  • Buy 1 bottle of Milk of Magnesia – The bottle of Milk of Magnesia will have 1200 mg magnesium hydroxide per 15 ml or 1 tablespoon. 
  • Buy 1 liter of Club Soda (unflavored and low sodium)

1.  Chill the club soda for 1 hour in the refrigerator.

2.  Shake the Milk of Magnesia well before using.

3.  Take club soda out of the refrigerator.

4.  Measure 3 Tbsp or 45ml of Milk of Magnesia.  Use plastic cap provided by manufacturer.  Three tablespoons is a total of 3600 mg of Milk of Magnesia in the 1 liter bottle of club soda.

5.   Pour the 3 TBSP – 45 ml of Milk of Magnesia into the 1 liter bottle. Replace the cap.

6.  Shake if 1 liter bottle vigorously for at least 1 minute or longer.  The sides of the plastic bottle may pull in when finished shaking. 

7.  Shake the bottle until all sediment has dissolved.   If there is some small sediment at the bottom of the bottle that is just unconverted Milk of Magnesia. 

8.  Place bottle back into the refrigerator.

The 1 liter bottle of magnesium bicarbonate is concentrated and should be diluted with water.  It is recommended to drink at least 4 ounces of the magnesium bicarbonate twice per day by adding it to your regular water consumption.


Water and the Human Body Series: Chapter 4 – Water Output by the Human Body

When the body is in a balanced and healthy state, or what is known as homeostasis, the body is not designed to store water.  However, if the body is in a diseased state, the body has means to store water.  (See Chapters on Dehydration, Hyponatremia and Edema -Fluid retention)

Water is being lost by the body on a constant basis, so the water content of the body is constantly changing.

Water loss from the human body is classified as either sensible loss or insensible loss.  Sensible” loss is loss that can be perceived by the senses and can be measured.  Insensible losses can neither be perceived nor measured directly. You’ve lost it, but you don’t know that you’ve lost it.

Sensible loss:

  • Through the kidneys (urine excretion)
  • Through the gastro-intestinal tract (feces)

Insensible loss:

  • Trans-epidermal diffusion: water that passes through the skin and is lost by evaporation (perspiration and sweating)
  • Evaporative water loss from the respiratory tract  (by breathing)

The quantity of water loss varies with the lifestyle and environmental conditions of the individual, such as, gender, body size, weather, clothing worn, activity levels and a whole range of other factors.  However, on average, a typical adult loses about 2.1 to 2.7 liters (L) of water per day, broken down as follows:

  • lungs     400–500 mL  (18.5%)
  • skin       400–500 mL  (18.5%)
  • stool      80–100 mL   (3%)
  • urine      1–1.6 L        (60%)

 Image result for human water output

Figure 1:  Average Intake and Output of water per day

An individual who engages in physical exercise or is in a hot environment will loss additional water via sweat.  The amount of additional water loss via sweat may be up to several liters per day.

The environmental factors that effect water loss for each bodily organ and system, include:

Skin and lungs – If the air is dry and hot, water loss is increased

Urine – Urine water loss is dependent on the volume of the fluid consumed and total losses by other routes.  Urine water loss is also dependent on sodium chloride content in the diet as well as protein consumption.  The more sodium chloride and protein consumed, the more water loss is decreased due to the limited capacity of the kidneys to concentrate the urine. If water intake is restricted, the kidneys will conserve water by producing a more concentrated urine.

To maintain a healthy homeostatic state, the intake of water should be more than the loss via skin, lungs and feces and the any surplus is excreted by the kidneys. Typically urinary volume largely depends on intake of water, which should exceed the average output, taking into consideration external factors such as exercise, diet and environment.

Previously published Chapters in the Series

Chapter 1 – Water Content in the Human Body

Chapter 2 – The Function of Water in the Human Body

Chapter 3 – Methods of Gaining Water into the Human Body

Future Chapters in the Series:

Chapter 5 – Water Balance in the Human Body

Chapter 6 – Dehydration

Chapter 7 – Waters Effect on Neurological Health

Chapter 8 – Edema – Fluid Retention

Water and the Human Body Series: Chapter 3 – Methods of Gaining Water into the Human Body

“Water does not stay in one place, it flows quickly and carves its own way, even through stone – and when something blocks its way, water makes a new path.”

— Memoirs of a Geisha

Three Methods of Gaining Water in the Body

There are 3 methods of gaining water in the human body:

  • Drinking water and other fluids (accounts for ~60%-70% of the total fluid gain)
  • Dietary intake of food  (accounts for ~30%-20% of the total fluid gain)
  • Metabolic water produced by human cells through cellular respiration  (accounts for ~10% of the total fluid gain)

Drinking water and other fluids

The most common way of adding water to the body is by drinking water or other fluids.  These other fluids will varying on the amount of water content, for example, pure water compared to vegetable juices. 

Some fluids may actually create a net fluid loss or at least not contribute to water gain in the body.  For example, ethanol or drinking water is approximately 60% water depending on the type of spirit, yet it can be a very dehydrating beverage in excess quantities and does not replenish water content in the human body.  

All water-containing drinks can contribute to the total required for hydration including fruit juice, soft drinks, tea, coffee, dilute alcoholic drinks such as beer, as well as pure water itself.

Dietary intake of food

Most foods, even those that look hard and dry, contain water. The body can get approximately 20 to 30 percent of its total water requirements from solid foods alone.

Living or raw foods have a higher content of water since they have not been cooked by heating.  Cooked foods usually have less water content, for example, cooked broccoli versus raw broccoli.  Processed foods may contain a very low water content and are not preferred in the diet for water gains.

The variety of the diet will dictate the amount of water consumed in the diet.  The higher the consumption of water-rich foods (e.g., fruits, vegetables or soup), the higher the intake of water from food. Fruits and vegetables are indeed the food group which contains the most water: from 96% in a cucumber to 72% in an avocado, most contain more than 85% water.

The Figures 1 and 2 below list the water content of various food:



Metabolic water

Metabolic water refers to water created inside a living organism through metabolism, by oxidizing energy-containing substances in their food. Humans obtain only about 8-10% of their water needs through metabolic water production.  

Each macronutrient that is metabolized in the body produces different quantities of water as a by-product.  Lipid (fat) oxidation produces the most water per gram.

The Table below illustrates the metabolic water production for all three macronutrients:   1

Metabolic Water from Macronutrients

Macronutrient in 100 gramsMetabolic Water Produced
Fat110 grams
Protein41.3 grams
Carbohydrate55 grams

One liter equals 1,000 grams, so 100 grams is the equivalent to 0.10 liters.

The amount of metabolic water produced by an average body is approximately 250 ml to 350 ml per day, depending on the variety of the diet.  Metabolic water production is proportional to the energy intake. As a result a sednetary individual may produce 250 ml of metabolic water per day versus a physically active individual engaging in strenuous exercise may produce up to 600 ml per day of metabolic water.

Metabolism of Water in the Body

Once water is ingested, it is absorbed in the gastrointestinal tract starting with the stomach in which a small portion is absorbed.  After leaving the stomach, water is absorbed mostly in the early segments of the small intestine, the duodenum and the jejunum. The small intestine absorbs about 6.5 liters per day and the colon absorbs about 1.3 liters per day.

From there the water enters the cardiovascular system by passing from the intestinal lumen into plasma mainly by passive transport, regulated by osmotic gradients.  The absorption process is very rapid where within 5 minutes after ingestion of water it us present in the plasma and blood cells. 

The vascular system then transports it to the interstitial tissue spaces between cells.  It then crosses the cell membrane via aquaporins, which are specific integral membrane proteins for water transport into the cell.

Image result for aquaporins

Figure 3:  Aquaporin illustration

Recommendations for daily water intake

Insufficient scientific research exists that addresses the issue of the amount of water required to prevent disease or improve health. Due to this no exact consumption thresholds clearly exist or are linked to a specific health benefit or risk.  However, there are a number of agreed upon guidelines as to the minimum amount of water to be consumed depending on a variety of factors, including age, weight, health status, gender, level of activity (exercise) and environment.

In 2010 the European Food Safety Authority (EFSA) published official guidelines for total water intakes.  These guidelines are based on physiological parameters based on age.  These recommendations assumes no physical activity which will account for extra fluid loss and will need to be restored.

The Table below lists the recommended adequate intake values for water:

Dietary Reference Values for Water

Age rangeDaily adequate water intake
0-6 months680  mL/day or 100-190  mL/kg/day. From human milk
6-12 months0.8-1.0  L/day. From human milk and complementary foods and beverages
1-2 years1.1-1.2  L/day
2-3 years1.3  L/day
4-8 years1.6  L/day
9-13 years – Males2.1  L/day
9-13 years – Females1.9  L/day
14-18 years – Males2.5  L/day
14-18 years – Females2.0  L/day
19-70 years – Males2.5  L/day
19-70 years – Females2.0  L/day
Special cases
Pregnant women2.3  L/day
Lactating women2.7  L/day

Source:  EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water. EFSA Journal 2010; 8(3):1459. [48 pp.]. doi:10.2903/j.efsa.2010.1459.

Previously published Chapters in the Series

Chapter 1 – Water Content in the Human Body

Chapter 2 – The Function of Water in the Human Body

Future Chapters in the Series:

Chapter 4 – Water Loss by the Human Body

Chapter 5 – Water Balance in the Human Body

Chapter 6 – Dehydration

Chapter 7 – Waters Effect on Neurological Health

Chapter 8 – Edema – Fluid Retention

Previously published Chapters in the Series

Chapter 1 – Water Content in the Human Body

Chapter 2 – The Function of Water in the Human Body

Future Chapters in the Series:

Chapter 4 – Water Loss by the Human Body

Chapter 5 – Water Balance in the Human Body

Chapter 6 – Dehydration

Chapter 7 – Waters Effect on Neurological Health

Chapter 8 – Edema – Fluid Retention

Cerebral Spinal Fluid: The Water of Life

The brain produces roughly 500 mL of cerebrospinal fluid per day. This fluid is constantly reabsorbed, so that only 100-160 mL is present at any one time.

The entire surface of central nervous system is bathed by a clear, colorless fluid called cerebrospinal fluid (CSF). The CSF is contained within a system of fluid-filled cavities called ventricles.

Neurogenesis is dependent on the CSF. New neurons are created and travel in the CSF. [ [i] ] Hydration is the key to the CSF. [ [ii] ]

Ependymal cells of the choroid plexus produce more than two thirds of CSF. The choroid plexus is a venous plexus contained within the four ventricles of the brain, hollow structures inside the brain filled with CSF. The remainder of the CSF is produced by the surfaces of the ventricles and by the lining surrounding the subarachnoid space.

CSF Flow

Circulation of CSF. CSF (gray) is secreted by the choroid plexus present in the cerebral ventricles and by extrachoroidal sources. It subsequently circulates through the ventricular cavities and into the subarachnoid space. Absorption into the venous blood (dark orange) occurs through the arachnoid villi in the superior sagittal sinus and along the optic, olfactory and spinal nerve sheaths

From: Blood—Cerebrospinal Fluid Barrier Cover of Basic Neurochemistry Basic Neurochemistry: Molecular, Cellular and Medical Aspects. 6th edition. Siegel GJ, Agranoff BW, Albers RW, et al., editors. Philadelphia: Lippincott-Raven; 1999. Copyright © 1999, American Society for Neurochemistry.

CSF serves several purposes:

1.  Buoyancy: The actual mass of the human brain is about 1400 grams; however, the net weight of the brain suspended in the CSF is equivalent to a mass of 25 grams. The brain therefore exists in neutral buoyancy, which allows the brain to maintain its density without being impaired by its own weight, which would cut off blood supply and kill neurons in the lower sections without CSF.

2.  Protection: CSF protects the brain tissue from injury when jolted or hit. In certain situations such as auto accidents or sports injuries, the CSF cannot protect the brain from forced contact with the skull case, causing hemorrhaging, brain damage, and sometimes death.

3.  Chemical stability: CSF flows throughout the inner ventricular system in the brain and is absorbed back into the bloodstream, rinsing the metabolic waste from the central nervous system through the blood–brain barrier. This allows for homeostatic regulation of the distribution of neuroendocrine factors, to which slight changes can cause problems or damage to the nervous system. For example, high glycine concentration disrupts temperature and blood pressure control, and high CSF pH causes dizziness and syncope. To use Davson’s term, the CSF has a “sink action” by which the various substances formed in the nervous tissue during its metabolic activity diffuse rapidly into the CSF and are thus removed into the bloodstream as CSF is absorbed.

4.  Prevention of brain ischemia: The prevention of brain ischemia is made by decreasing the amount of CSF in the limited space inside the skull. This decreases total intracranial pressure and facilitates blood perfusion.

5.  Clearing waste: CSF has been shown by the research group of Maiken Nedergaard to be critical in the brain’s glymphatic system, which plays an important role in flushing metabolic toxins or waste from the brain’s tissues’ cellular interstitial fluid (ISF). CSF flushing of wastes from brain tissue is further increased during sleep, which results from the opening of extracellular channels controlled through the contraction of glials cells, which allows for the rapid influx of CSF into the brain. These findings indicate that CSF may play a large role during sleep in clearing metabolic waste, like beta amyloid, that are produced by the activity in the awake brain.

6.  Endocrine medium for the brain: the CSF serves to transport hormones to other areas of the brain. Hormones released into the CSF can be carried to remote sites of the brain where they may act.

Typical Cerebrospinal Fluid (CSF) and Plasma Concentrations of Various Substances

SubstanceCSFPlasmaCSF/plasma ratio
Electrolytes (mEq/l)
Metabolites (mM)
Amino acids (μM)
  Aspartic acid0.22.00.1
  Glutamic acid26.161.30.4
Proteins (mg/l)
  Total protein35070,0000.005
From: Constancy of the Internal Environment of the Brain
Basic Neurochemistry: Molecular, Cellular and Medical Aspects. 6th edition.
Siegel GJ, Agranoff BW, Albers RW, et al., editors.
Philadelphia: Lippincott-Raven; 1999.
Copyright © 1999, American Society for Neurochemistry

The Table below lists the researched substances that enhance the cerebral spinal fluid:

Substances that Enhance the Cerebral Spinal Fluid

Amino Acid


[i] Neurogenesis at the Brain–Cerebrospinal Fluid Interface

[ii] Investigating Structural Brain Changes of Dehydration Using Voxel-Based Morphometry

Daniel-Paolo Streitbürger, Harald E. Möller, Marc Tittgemeyer, Margret Hund-Georgiadis,

Matthias L. Schroeter, Karsten Mueller Published: August 29, 2012 DOI: 10.1371/journal.pone.0044195

Dehydration confounds the assessment of brain atrophy, T. Duning, MD, S. Kloska, MD, O. Steinsträter, PhD, H. Kugel, PhD, W. Heindel, MD and S. Knecht, MD

Dehydration affects brain structure and function in healthy adolescents

Effects of fluid ingestion on cognitive function after heat stress or exercise-induced dehydration

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Water and the Human Body Series: Chapter 2 – The Function of Water in the Human Body

Review Chapter 1 – Water Content in the Human Body

The function of water in the body is extremely important.  In fact, water in the human body is the giver of life.  Without water, life would cease to exist.

Water helps nearly every part of the human body function efficiently. If water is 60% of the human body mass, it is vital to understand the functions of water in the human body and how a deficiency of water may cause a compromise to human health.

Following is a list of some of the more important functions of water in the human body:

Water provides cellular communication

Thoughts, emotions, nervous system transmission thought to be transmitted by water. Making water the primary mode of cellular communication.

Water is required for brain function

The brain receives 15-20% of the blood supply which is mostly comprised of water.  The cerebrospinal fluid  is critical for proper brain function.

Water is needed for bone function

Bones require plentiful supplies of water. The upper body is is supported by the water core contained within the fifth lumbar disc and muscle fibers around the spine.

Water is needed for nerve function

Microtubules, which are microstreams of water, carry water to the synapses to transmit messages.

Water is a nutrient carrier to cells

Water is a carrier, distributing essential nutrients to cells, such as minerals, vitamins and glucose.

Water is a required in chemical and metabolic reactions

Chemical reactions within the body and metabolism is critically dependent on water and a lack of water in the human body means incomplete or faulty metabolic processes.

Water is required for proper detoxification

Water removes waste products including toxins that the organs’ cells reject, and removes them through urines and feces.

Water regulates body temperature

Water has a large heat capacity which helps limit changes in body temperature in a warm or a cold environment. 

Water protects tissues, spinal cord, and joints

Water keeps the tissues in the body moist and helps protect the spinal cord  It also acts as a lubricant and cushion for joints. It also acts as a shock absorber for eyes, brain, spinal cord and even for the fetus through amniotic fluid.

Water aids in digestion

Water is the main solvent for all foods, vitamins and minerals. It is used in the breakdown of food into smaller particles and their eventual metabolism and assimilation.

Digestion starts with saliva, which primarily consists of water. 

Water acts as a solvent 

Water is the fundamental solvent for all biochemical processes in our bodies.  Because water is highly polar (has an unequal distribution of charge), it is an excellent solvent for other charged and polar molecules. 

Water acts as a transporter

Once a substance is dissolved in water, water becomes very important for transporting it throughout the body.  Blood, which is 83 percent water, transports oxygen, CO2, nutrients, waste products, and more from cell to cell.  Urine removes waste products from the body.  

Water regulates pH balance

Adequate levels of water in the human body help regulate pH balance and maintains a specific pH level of around 7.4.  

Water regulates electrolyte balance

Electrolytes are important charged ions that must be kept at certain levels in order to maintain the proper amount of water in the cells. To maintain electrolytes at the proper level in our cells, water flows in and out of the cell to make sure that these ions remain in balance.  Electrolytes transmit all sorts of information to our brains in the form of nerve impulses and are important in muscular activity as well.

Additional Functions of water in the Human body:

Water is required for breathing

Water moistens oxygen for breathing

Water dilutes the blood and prevents it from clotting during circulation

Water moistens mucous membranes such as those of the lungs and mouth

Water reduces the risk of cystitis by keeping the bladder clear of bacteria

Water moisturizes the skin to maintain its texture and appearance

Water increases the efficiency of red blood cells in collecting oxygen in the lungs

Water helps reverse addictive urges, including those for caffeine, alcohol and some drugs

Water is used in the spinal discs to make them “shock absorbing water cushions”

Water prevents clogging of arteries in the heart and the brain

Water gives us power and electrical energy for all brain functions, most particularly thinking

Water prevents DNA damage and makes its repair mechanisms more efficient 

Water increases greatly the efficiency of the immune system in the bone marrow, where the immune system is formed

Water keeps the bloodstream liquid enough to flow through blood vessels

Water is directly needed for the efficient manufacture of all neurotransmitters, including serotonin

Water is directly needed for the production of all hormones made by the brain, including melatonin

Water restores normal sleep rhythms

Water prevents the loss of memory as we age. It helps reduce the risk of Alzheimer’s disease, multiple sclerosis, Parkinson’s disease and Lou Gehrig’s disease


Previously published Chapters in the Series

Chapter 1 – Water Content in the Human Body

Future Chapters in the Series:

Chapter 3 – Water Gain (Consumption) in the Human Body

Chapter 4 – Water Loss by the Human Body

Chapter 5 – Water Balance in the Human Body

Chapter 6 – Dehydration

Chapter 7 – Waters Effect on Neurological Health

Chapter 8 – Edema – Fluid Retention

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Water and the Human Body Series: Chapter 1 – Water Content in the Human Body

Water is the largest single component of the human body, accounting for about 50–60% of total body mass. For a healthy lean young male with a body mass of 70 kg (154lbs), total body water will consist of about 42 liters. A healthy lean young woman is about 50% of total body mass. This is due to a women typically having less skeletal muscle and more body fat than males.

Water makes up between 45 and 75% of body weight, with the variability due primarily to differences in body fat. While most tissues including muscle, skin, and visceral organs are over 75% water, adipose tissue contains less than 10% water.

Water is also contained inside organs, in gastrointestinal, cerebrospinal, peritoneal, and ocular fluids.

The gender differences, from the teenager years onwards, are due to their differing fat levels, as is the drop in the elderly who replace muscle mass with fat. There is little difference with gender or age from childhood onwards, if allowance is made for this fat content.

The estimation of body water will vary with factors such as

  • Type of population
  • Number of people sampled
  • Age of people sampled
  • Body fat percentage

Variation due to Age

Neonates contain more water than adults: 75-80% water with proportionately more extracellular fluid (ECF) then adults. At birth, the amount of interstitial fluid is proportionally three times larger than in an adult. By the age of 12 months, this has decreased to 60% which is the adult value.

Total body water as a percentage of total body weight decreases progressively with increasing age. By the age of 60 years, total body water (TBW) has decreased to only 50% of total body weight in males mostly due to an increase in adipose tissue.

For both men and women, the percent of body weight that is water decreases with age:

  • Fetus – 90% of total weight
  • Infant – 74% of total weight
  • Child – 60% of total weight
    • Teenager
      • Male 59% of total weight
      • Female 56% of total weight
  • Adult
    • Male 59% of total weight
    • Female 50% of total weight
  • Adult over 50 years
    • Male 56% of total weight
    • Female 47% of total weight


Variation by Body Fat Percentage

Adipose (fat) tissue is the least hydrated tissue in the body (20% hydrated), even bone contains more water than fat. In contrast, skeletal muscle contains 75% water. So, the more muscles one has, the higher the total body water percentage will be.

The so-called lean body mass, which means a body stripped of fat, contains 0.69 parts of water (69%) of the total body weight in all persons. – Such high values are observed in the newborn and in extremely fit athletes with minimal body fat. Babies have a tenfold higher water turnover per kg of body weight than adults do.

As an average females have a low body water percentage compared to males. Such differences show sex dependency, but the important factor is the relative content of body fat, since fat tissue contains significantly less water (only 10%) than muscle and other tissues (70%). This is why the relative water content depends upon the relative fat content.

The percentage of body weight that is water therefore varies inversely with body fat. In the average lean adult male around 60% of the body weight is water. The remaining body weight consists of 16-18% fat with 22-24% protein, carbohydrate and other solids. In the female the percentage of body weight that is water is lower due to a relatively greater amount of subcutaneous fat.

Variation between Tissues

Most tissues are water-rich and contain 70-80% water. The three major exceptions to this are:

  • Plasma: 93% water (and 7% ‘plasma solids’)
  • Fat: 10-15% water
  • Bone: 20% water

Fluid Compartments of the Human Body

Fluid compartments in the human body broadly comprise two compartments, each with several subdivisions:

  • The Intracellular Fluid (ICF)
  • The Extracellular Fluid (ECF)


The Intracellular Fluid (ICF)

The intracellular fluid (ICF) is about 40 % of body weight and is contained within the various cells of the body. Intracellular fluid (ICF) makes up approximately 60-65% of total body water.

The ICF is the fluid that is confined within the cell membranes. Intracellular fluid is found inside the two-layered plasma membrane of the body’s cells, and is the matrix in which cellular organelles are suspended, and chemical reactions take place. In humans, the intracellular compartment contains on average about 28 liters of fluid.

The Extracellular Fluid (ECF)

The extracellular fluid (ECF) makes up 35-40% of total body water.

Extracellular fluid (ECF) or extracellular fluid volume (ECFV) usually denotes all body fluid outside of the cells. The volume of extracellular fluid is typically 15 liters where 12 liters is interstitial fluid and 3 liters is plasma).

The ECF is divided into several smaller compartments:

  • Plasma
  • Interstitial fluid
  • Fluid of bone and dense connective tissue and
  • Transcellular fluid

These compartments are distinguished by different locations and different kinetic characteristics. The composition of ECF is high in sodium and chloride and low in potassium and magnesium.

Plasma is the only major fluid compartment that exists as a real fluid collection all in one location. It differs from ISF in its much higher protein content and its high bulk flow (transport function). Blood contains suspended red and white cells so plasma has been called the ‘interstitial fluid of the blood’.

Interstitial fluid (ISF) consists of all the bits of fluid which lie in the interstices of all body tissues. This is also a ‘virtual’ fluid meaning that it exists in many separate small bits but is spoken about as though it was a pool of fluid of uniform composition in the one location.

The ISF bathes all the cells in the body and is the link between the ICF and the intravascular compartment. Oxygen, nutrients, wastes and chemical messengers all pass through the ISF.

Lymph is considered as a part of the ISF. The lymphatic system returns protein and excess ISF to the circulation.

The fluid of bone and dense connective tissue is significant because it contains about 15% of the total body water. This fluid is mobilized only very slowly and this lessens its importance when considering the effects of acute fluid interventions.

Trans-cellular fluid is a small compartment that represents all those body fluids which are formed from the transport activities of cells. It is contained within epithelial lined spaces.

It includes cerebral-spinal fluid (CSF), gastrointestinal tract fluid (GIT), bladder urine, aqueous humour and joint fluid. It is important because of the specialized functions involved. The fluid fluxes involved with GIT fluids can be quite significant.


Typical values for the size of the fluid compartments are listed in the table below.

Body Fluid Compartments (70 kg male)

Body Fluid Compartments

% of Body

% of Total
Body Water














Dense CT water




Bone water















42 liters

Future Chapters in the Series:

Chapter 2 – The Function of Water in the Human Body

Chapter 3 – Water Gain (Consumption) in the Human Body

Chapter 4 – Water Loss by the Human Body

Chapter 5 – Water Balance in the Human Body

Chapter 6 – Dehydration

Chapter 7 – Waters Effect on Neurological Health

Chapter 8 – Edema – Fluid Retention

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The Effects of Dehydration on the Brain

“Dehydration increases the osmolality of extracellular fluid in the body and decreases blood volume [Costill et al., 1976]. Both are processes that could reduce total brain volume and lead to a corresponding increase in CSF volume. Increased concentrations of solutes in extracellular fluid cause water to move from inside cells to the extracellular fluid along the osmotic gradient, causing cellular shrinkage [Gullans and Verbalis, 1993]. However, cells prevent large increases and decreases in volume by actively regulating their intracellular solute (particularly potassium ions), which is of vital importance in the brain because of the fixed volume of the cranium [Stricker and Verbalis, 2003]. Indeed, if such homeostatic processes were not active we might expect to see larger changes in brain structure following dehydration. As brain volume decreases, the empty space is filled by CSF; this may come from an increase in production or a decrease in absorption of CSF, or from the CSF filled spinal dural sack which unlike the cranium, can change its volume in response to intracranial pressure [Lee et al., 2001; Lofgren and Zwetnow, 1973].”

From Effects of acute dehydration on brain morphology in healthy humans, Matthew J. Kempton1,2,*, Ulrich Ettinger1, Anne Schmechtig1, Edward M. Winter3, Luke Smith4, Terry McMorris4, Iain D. Wilkinson5, Steven C.R. Williams1 and Marcus S. Smith4. Human Brain Mapping

Neurons store water in tiny balloon-like structures called vacuoles. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain cases they may contain solids which have been engulfed.

Water is essential for optimal brain health and function. Water is necessary to maintain the tone of membranes for normal neurotransmission. It enhances circulation and aids in removing wastes.

Microtubules in the neuron is filled with water. [1] Microtubules are tiny sub-components of cells. They are prominent aspects of the skeleton of all eukaryotic cells and are the structural and dynamical basis of the cells. They may participate in important quantum mechanical phenomena involving water ordering in their interior.

Microtubules contribute to the structural integrity of neurons as they maintain the semi-rigidity of neurons.

There are various substances that may interfere with microtubules:

  • Acetaldehyde may inhibit the ability of tubulin to assemble into microtubules. [2]
  • Mercury may disrupt the structural integrity of neuronal microtubules. [3]