The human body can survive without food for many months, but without water only for a few days.
As you may guess, water is the most precious component of our diet, and is only antagonized by the even more essential oxygen.
The average adult’s bodyweight consists of 55-75% water.
In particular, water comprises 70-75% of muscle tissue and 10-40% of fat tissue.
Water’s biological role is crucial for the development and maintenance of life on earth, and possibly other planets.
If there was no water there would be no life on earth
This is attributed to its capability of dissolving more substances than any other liquid, giving it the nickname- the “universal solvent” as its versatility and adaptability help perform many important chemical reactions
Water’s Role in Human Health
Water is an essential component of cellular homeostasis and life in general.
It acts as a nutrient transporter, lubricates joints and internal organs, provides structure to cells and tissues, helps preserve cardiovascular function and comprises 90% of our blood.
Comprised of two molecules of hydrogen and one oxygen (H2O), water is a chemical compound necessary for the body to facilitate its daily, basic biochemical processes:
- Nutrient transportation- No cells can survive without water, as food constituents and other chemical substances can not reach their destination.
- Temperature regulation, as it is a constituent of sweat, which is secreted on to the skin and evaporates, cooling the body surface.
- Dead cell and toxin elimination, as it dilutes them and escorts them out of the body through the feces, urine and sweat.
- Cell membrane regeneration.
- Joint and muscle flexibility, as the synovial fluid lubricating the joints is made up primarily of water.
- Hydrolyzation of various substrates, such as protein, carbohydrates, and fats.
- Moistening of food for swallowing, as our saliva is 99.5% water.
Water Homeostasis and Fluid Balance
Most of the components of fluid balance are controlled by homeostatic mechanisms responding to the water status of the body.
These mechanisms are very delicate and precise, and get stimulated with deficits or excesses of water amounting to only a few hundred milliliters (ml).
A water deficit produces an increase in the ionic concentration of the extracellular compartment, which takes water from the intracellular compartment causing cells to shrink.
This shrinkage is detected by two types of brain sensors, one controlling drinking and the other controlling the excretion of urine by sending a message to the kidneys, mainly via the antidiuretic hormone vasopressin (AVP) to produce a smaller volume of more concentrated urine .
Put simply, maintaining a constant water and mineral balance requires the coordination of sensitive detectors at different sites in the body, which are linked by neural pathways with integrative centers in the brain processing the incoming information.
These centers respond with the production of neuroendocrine compounds that regulate urination (diuresis), sodium excretion through the kidneys (natriuresis) and blood pressure (angiotensin I & II, mineralocorticoids, vasopressin, atrial natriuretic factor).
Water and fluid balance is tightly regulated by the action of the neuroendocrine system, specifically the hormonal communication between the hypothalamus, the pituitary gland, the adrenal glands, and kidneys.
Dehydration Causes and Symptoms
Dehydration refers to an imbalance between water intake and water loss, and is characterized by a decrease in total body water content due to fluid loss, diminished fluid intake, or both.
The most common side effects of dehydration are:
- Dry lips
- Dry tongue
- Dry skin
- Decreased urination
- Depression and Anxiety
- Lack of motivation
- Lack of focus
- Muscle weakness
- Rapid breathing
- Muscle cramps
The most common causes of dehydration are:
- Flight travel
Hormonal Responses to Dehydration
When the body senses dehydration, it responds in two primary ways:
1) Baroreceptor Activation and Vasopressin Secretion
- Inadequate water intake results in an abnormal decrease in blood volume and blood pressure, which stimulates the baroreceptor neurons in the aorta and carotid sinuses.
- Baroreceptor activation leads to increased secretion of vasopressin/anti-diuretic hormone (ADH) from the posterior pituitary gland (ADH is originally produced by hypothalamic neurons and then stored in the posterior pituitary).
- ADH increases water re-absorption in the kidneys.
2) Renin-Angiotensin-Aldosterone System
- Insufficient water intake provokes a drop in both blood pressure and blood volume, which stimulates the juxtaglomerular cells in the kidneys to convert the precursor molecule prorenin (already present in the circulation) into renin, and secrete it directly into the blood.
- Renin converts the precursor angiotensinogen -released by the liver – to angiotensin I.
- The lung endothelial cells release the angiotensin-converting enzyme (ACE), which converts Angiotensin I to Angiotensin II.
- Angiotensin II stimulates the secretion of aldosterone from the adrenal cortex and promotes the constriction of arterioles.
- The release of aldosterone increases the reabsorption of salt and water in the kidneys.
Water and Weight Loss
Studies have found an association between adequate water consumption and healthy weight management .
Water, especially cold water, stimulates the metabolism and supports weight loss .
It does that through increasing blood circulation, which increases body temperature and BMR (water thermogenesis) .
Studies show that drinking water increases the basic metabolic rate (BMR) of adults by 24–30% within 60 minutes of ingestion .
Also, it has also been found that in conjunction with a hypocaloric diet, drinking 500 ml. of water prior to a meal helps people consume fewer calories and lose weight, via decreasing appetite and reducing energy intake .
Water promotes a healthy weight long term as studies have found that its substitution with other beverages, such as coffee, tea, diet beverages, low-fat and whole milk, lead to unwanted body fat accumulation .
Besides, water consumption in comparison with not drinking at all or drinking other types of beverages, has been proposed to be an effective precautionary measure against obesity .
A German study conducted in elementary schools of socially deprived areas, found that supplying children with adequate water intake can greatly assist them in sustaining a normal, healthy weight.
The study showed that children who drink enough water are less likely to become overweight by as much as 31% .
Water and Detoxification
Ingestion of large amounts of water supports the kidneys and liver, helping the body to remove toxins and cellular by-products of metabolism.
Increased water intake can mitigate the effects of toxemia (high load of toxins in the bloodstream), diluting them, and stimulating the eliminative organs to expel them (kidneys, large bowel, skin).
Water fasting, which means complete abstinence from food, while drinking nothing but water, is one of the cheapest, most effective ways to rapidly clean and detoxify the body, as well as addressing metabolic disorders (i.e insulin resistance, metabolic syndrome, etc).
Water fasting is a spiritual practice that goes back centuries; Jesus Christ was said to fast for 40 days.
Alternative doctors are over the world utilize water fasting for their chronically, sick patients.
Water fasting offers rest to the digestive system, which is a very busy organ system that rarely gets a break.
Fasting activates ancient biochemical pathways within the human body that promote healing and regeneration:
- Stabilizes blood sugar 
- Enhances insulin sensitivity 
- Improves blood lipid status (HDL, LDL, triglycerides, cholesterol) [4, 5]
- Boosts brain function and improve neurogenesis [6, 7]
- Aids in weight loss and temporarily increase metabolic rate [8, 9]
- Increases growth hormone secretion, which is necessary for muscle growth, skin elasticity and cell renewal [10, 11]
- Delays aging and increases longevity [12, 13, 14]
- Upregulates the immune system, which can more effectively detect and kill potential cancer cells 
- Makes the person more resilient to the side-effects of chemotherapy 
Water and Athletic Performance
If you are not adequately hydrated your muscle contractions and overall physical performance will suffer.
This is particularly evident in high ambient temperatures during the summer months, and is attributed to the increased rates of sweating.
Dehydration can have a noticeable negative effect on your performance even if you lose just as two percent of your body’s water content .
Athletes tend to lose a lot of water during their athletic endeavors. It’s not uncommon for some to lose as much as six to ten percent of their total body weight through sweating.
Nonetheless, water loss doesn’t happen only during urination and sweating, but also insensibly through perspiration.
Dehydration affects both the physiology of muscle tissue as well as the athlete’s brain.
In a 2012 study of 25 young women, researchers found that fluid loss of only 1.4 percent after exercise impaired both mood and concentration .
Some members of the research team that studied the women also conducted a similar study in young men in 2011 .
They found that fluid loss of 1.6 % was detrimental to working memory and increased feelings of anxiety, fatigue and tension.
A fluid loss of 1.3% equals about 1.5 to 4.5 of body weight loss in an average person weighing 150 lbs.
This can easily occur through normal daily activities and certainly through exercising in high heat conditions.
Optimal hydration prevents all these side-effects and has also been shown to decrease oxidative stress- the waste products of oxygen metabolism- which can damage cell constituents if present in high enough amounts.
Oxidative stress occurs greatly during high-intensity exercise and is a known cause of muscle fatigue .
The Brain-Hydration Connection
The brain is the fattiest organ of the body consisted of over 60% fat.
It is also – along with the heart- one of the most water-rich organs, comprised of 73% water.
Hydration status greatly affects brain performance.
In adults, water ingestion following a period of fluid restriction and/or fasting was repeatedly found to enhance the state of arousal, increasing cognitive dimensions such as alertness, attention and reaction time, and decreasing perception of confusion .
Studies show that mild dehydration, in the range of 1 to 3% of body weight can impair many aspects of brain function, like memory, mood and concentration in both young and old individuals .
Also, dehydration can produce delirium episodes in older people, often resembling the symptoms of Alzheimer’s disease 
Dehydration decreases blood volume (since blood is 90% water), causing inadequate oxygen and nutrient delivery to the brain, creating what-looks-like a dementia crisis.
Dehydration can also trigger headaches and migraines.
Research has shown that headaches are one of the most common symptoms of dehydration and that by simply drinking more water, people suffering from frequent headaches can find substantial relief .
Water Intake Recommendations
You must have probably heard the traditional recommendation to drink 8 glasses of water per day (the famous 8×8 rule).
While this notion is arbitrary, erroneous and of unknown origin, you should definitely strive to attain adequate levels of hydration each day.
Typically, the average adult should consume about 2-3 liters of water per day; Specifically, 2.2 liters for women and 3 liters for men.
Of course, this number often is subjective and depends on the person’s diet, physical activity, energy expenditure, and ambient temperature (i.e. high environmental temperatures require a higher water intake).
Also, a diet rich in raw fruits and vegetables reduces water needs as opposed to a diet of overcooked and processed food.
Best Water Sources
In most countries, water is artificially fluoridated and chlorinated (and therefore should be avoided), making the use of a water filter often necessary.
A good water filter will remove impurities and dangerous substances, such as halogens (fluoride, chloride), solvents, pesticide residues, disinfection byproducts, and heavy metals (arsenic, lead, cadmium, cobalt, mercury).
We recommend the gravity-fed Watens water filter, because it removes 99% of halogens (including fluoride and chlorine), heavy metals, pathogens, odors and other toxins.
It’s also affordable and very easy to use.
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Watens Water Filter
Apart from filtered water, there are other types of commercially available, high-quality water you can enjoy, such as:
Spring water comes from a natural underground source that is geologically and physically protected, and must be collected at the spring before it’s put into a bottle.
It is chemically untreated, safe to drink at the place of origin, and has a nice, refreshing taste, rarely tasting flat or boiled.
Mineral water comes from a well and differs from the other types due to its high content of naturally occurring minerals and trace elements.
According to the law, nothing additional can be added to mineral water. The types and amounts of its minerals – like calcium, sodium, magnesium, potassium and sulfates – depend on its place of origin.
Thus, its potential health benefits and flavor can vary greatly. Its source should always be named on the bottle.
Purified water can come from any source but must be highly treated.
Examples include reverse osmosis, distilled and de-ionized water.
Its mineral content is inferior to that of spring or mineral water, but the purification process renders it free of toxic metals and chemicals.
Consuming solely this type of water may contribute to mineral deficiencies in the long term as it is de-mineralized and vigorously filtered.
Alkaline water is water with a more alkaline/basic pH than regular water.
By adding alkaline compounds such as various salts and metals, the water becomes more basic/alkaline reaching a pH of 8 or 9 as opposed to tap water’s pH of 7.
There is no scientific evidence supporting that alkaline water provides any special health benefits, nor that it systemically alkalizes an acidic body.
Artesian water, also known as “artesian-well drinking water”, comes from a well that taps a specific layer of rock or sand through which the water flows and is stored.
Essentially, its main difference to the other types of water coming from springs and wells is that it comes from a tapped aquifer.
Making sure you are drinking enough water is more important than the type of water you prefer.
There are many conflicting opinions on what type of water is best for health.
The most important thing to keep in mind is that your water should be free from added synthetic chemicals, like halogens (fluoride, chlorine, etc).
Fluoride interferes with the function of the thyroid gland and impairs cognitive performance .
It increases the concentration of thyroid-stimulating hormone (TSH) and decreases T3 and T4 production .
Chlorine also negatively affects the thyroid, antagonizing the uptake of iodine, which is necessary for the conversion of the inactive T4 to the active T3, leading to an underactive thyroid (hypothyroidism).
Other Sources of Water
Water can be obtained not only directly as a drink but from food and to a very small extent from the oxidation of macronutrients – whether ingested through food or from our own body fat (metabolic water).
We present the ranges of water percentages of various foods in the board below:
Water Content of Various Foods
|Water Percentage||Food Item|
|90-99%||Fat-free milk, cantaloupe, strawberries, watermelon, lettuce, cabbage, celery, spinach, pickles, squash (cooked)|
|80-89%||Fruit juice, yogurt, apples, grapes, oranges, carrots, broccoli (cooked), pears, pineapple|
|70–79%||Bananas, avocados, cottage cheese, ricotta cheese, potato (baked), corn (cooked), shrimp|
|60–69%||Pasta, legumes, salmon, ice cream, chicken breast|
|50–59%||Ground beef, hot dogs, feta cheese, tenderloin steak (cooked)|
|30–39%||Cheddar cheese, bagels, bread|
|20–29%||Pepperoni sausage, cake, biscuits|
|10–19%||Butter, margarine, raisins|
|1–9%||Walnuts, peanuts (dry roasted), chocolate chip cookies, crackers, cereals, pretzels, taco shells, peanut butter|
Water is a vital component of all living organisms and adequate hydration is essential for human health and well-being.
The modern human usually ignores the importance of sufficient water intake.
Drinking sodas, coffees, energy drinks, and various other beverages has become the new norm in our advanced, fast-paced society.
Most individuals don’t acknowledge the actual side-effects of inadequate hydration which can manifest as stomach aches, joint pains, headaches, migraines, hypertension, lethargy, fatigue, decreased motivation, depression, melancholy, weight problems and constipation.
A high intake of fruits and vegetables can decrease an individual’s water needs, as well as can living in low ambient temperatures, where the incidence of sweating is lower.
The most important precaution concerning water drinking is the avoidance of halogens (like chlorine and fluoride), which in many countries are synthetically added to the public water supply.
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About George Kelly
George Kelly M.Sc is a Sports Nutritionist, Functional Nutritional Therapy Practitioner (FNTP), and Metabolic Type expert. He is the CEO and lead author of Metabolic Body.
This content is for informational and educational purposes only. It is not intended to provide medical advice or to take the place of such advice or treatment from a personal physician. All readers/viewers of this content are advised to consult their doctors or qualified health professionals regarding specific health questions. Neither Metabolic Body nor the publisher of this content takes responsibility for possible health consequences of any person or persons reading or following the information in this educational content. All viewers of this content, especially those taking prescription or over-the-counter medications, should consult their physicians before beginning any nutrition, supplement or lifestyle program.