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Chapter: 11th 12th std standard Class Nursing Health Care Hospital Hygiene Higher secondary school College Notes

Water in Human Body

Water is vital for human existence. We can live with out food for extended periods of time, but without water will result in death.



Water is vital for human existence. We can live with out food for extended periods of time, but without water will result in death.


Water is colourless, calorie less compound of hydrogen and oxygen that virtually every cell in the body needs to survive. Water is closer being a universal solvent than any other compound.

Water is the largest single compound of the body and it is distributed as follows.

Distribution of water in the body

1. Intracellular water

(Present inside the cell)


2.Extracellular water

(present outside the cell)



(Present as plasma of blood)



(Present outside the blood vessels)



          (i) Interstitial fluid

          ( between the cells)

          (ii) Lymph

          (iii) Water present in brain,aqueous humor of the eye, pericardium, pleural cavities.

Total body water content is mainly determined by total amount of salt in the body. Salt and water concentration in the body is controlled by the kidneys.




1.     It is an essential constituent of all the cells of the body and the internal environment.

2.     Serves as a transport medium by which most of the nutrients pass into the cells and removes excretory products.


3.     Water is a medium for most biochemical reactions within the body and sometimes a reactant.

4.     It is a valuable solvent in which various substances such as electrolytes, non - electrolytes, hormones, enzymes, vitamins are carried from one place to another.


5.     Plays a vital role in the maintenance of body temperature. Heat is produced when food is burnt for energy. Body temperature must be kept at 80 - 108 Fahrenheit for higher or lower body temperature will cause death. Body heat is lost through the skin, lungs, urine and faeces.

6.     It forms a part of fluids in body tissues; (eg) the amniotic fluid surrounds and protects the foetus during pregnancy.

7.     Saliva is about 99.5 percent water. In healthy individuals it makes swallowing easier by moistening the food.

8.     Water helps in maintaining the form and texture of the tissues.

9.     Water is essential for the maintenance of acid base and electrolyte balance. It should be noted that pure water consists of hydrogen ion (H+) and hydroxyl ion (OH-).


Substances dissolve in water as ions with positive and negative charge. They are called electrolytes. The common electrolytes in our body are sodium, potassium and chloride.


Changes in electrolyte balance causes accumulation or depletion of water in intracellular and extra cellular fluid.

The balance between the positively and negatively charged ions is essential for water flow and maintain osmolarity between the cells. This is called electrolyte balance.


Acid base balance is the dynamic state of equilibrium of hydrogen ion concentration. When pH falls below 7 it is termed acidity and when it increases above 7 it is termed alkalinity.


Extremes of both cases results in death. The pH of the body should be maintained near neutrality. Enzymatic action depends on the pH. The digestion, absorption and utilization of nutrients are dependent on pH. Most body fluids are near neutral with the exception of gastric juice.


The pH value of some solutions are given below:


0 - Hydrochloric acid


2 - Gastric juice

3 - Vinegar, orange juice

4 - Grapes

5 - Bread, coffee

--Neutral ------

6 - Urine

7 - Pure water, eggs, blood

8 - Sea water

14 - Sodium

---hydroxide Alkali---

Water forms good source of macro minerals like Calcium, Magnesium, Fluoride, Iron and Iodine.



Requirements of water varies with climate, dietary constituents, activities and surface area of the body. As a rule a person should take enough water to excrete about 1200 -1500 ml of urine per day. In tropics because of greater water loss through perspiration increased water intake is required to maintain urine volume. Normal intake of water ranges between 8 - 10 glasses per day.

Daily Water Input


In tropical countries like India the daily water input amounts to 2400 - 3000 ml of water through food, as fluid drinks and as metabolic water.

1.       As fluid drinks - water, tea, coffee, 

          milk soups  1500  - 1750 ml

2.       Water intake through solid food       600    -        900 ml

3.       Oxidation of carbohydrate, fat,         300    -        350 ml

          proteins (metabolic water)                         

                                      Total 2400 - 3000 ml

Daily output of water

1. Urine      1200  - 1500 ml   (kidney)

2.       Perspiration         700    -        900 ml        (Skin)

3.       Respiration 400 ml                           (lung)

4.       Faeces         100    -        200 ml                  (intestine)

Total 2400 - 3000 ml

Therefore the water intake and output is fairly kept constant. This is called water balance. The average adult metabolises 2.5 - 3.00 litres of water and a constant balance is maintained between intake and output. Inadequate water intake disturbs water equilibrium resulting in decreased urinary output, thereby causing changes in Extra Cellular Fluid (ECF) and Intra Cellular Fluid (ICF). The water equilibrium is maintained by kidneys, lungs, intestine and pituitary gland. The water balance coordinates with both electrolyte and acid base balance.




Causes :


When water is constantly lost from the body as in severe vomiting, diarrhoea, excessive sweating or excessive urine formation due to treatment with diuretics, the total water content of the body is reduced. Extra cellular and intra cellular fluid decreases leading to dehydration.


Effects of dehydration

1.     Tongue is dry.

2.     Pinch test is done by raising and releasing the skin. Slow return of skin to original position indicates decreased ECF.

3.     Decrease in plasma volume reduces cardiac output and may lead to cardiac failure.




Dehydration can be prevented by taking sufficient amounts of water as fluids. The correction of dehydration is called rehydration.


Oral rehydration therapy


It is the administration of fluid to prevent or correct dehydration.

Oral rehydration salt


WHO, UNICEF formula consist of the NaCl - 3.5 g, NaHCO3 - 2.5 g, KCl - 1.5g and glucose - 20 g to be dissolved in one litre of potable drinking water.


The Glucose present aids in the absorption of sodium chloride and potassium chloride apart from giving energy. This mixture is administered through the oral route at frequent intervals until the normal state is attained.


Potable water is that water which is safe and wholesome. It should be:


1.     free from pathogenic agents


2.     free from harmful chemical substance


3.     pleasant to taste; free from colour and odour


4.     usable for domestic purpose.


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