Sources and Losses of Water to Our Body

Sources of Water:

Water is supplied to our body in three main ways:

    i. The intake of water and beverages
    ii. The water present in foods
    iii. The water resulting from the oxidation of food in our body.

Losses of Water:

The daily loss of water has been shown in below table. Some loss of water is essential for the maintenance of physio-chemical equilibrium. These include the loss in faeces, through the lungs and insensible perspiration.

Renal Losses:

The amount of water lost from the kidney depends upon the amount of waste that must be excreted. Under normal circumstances, it is about 600 ml. Urea and sodium chloride are the principal solids that are excreted. A diet that is high in carbohydrate will minimize tissue catabolism and a low diet in protein is one that reduces the formation of urea and thus will spare body water.


Insensible perspiration accounts for a relatively constant amount of water loss that is proportional to the surface area of the body. It is called ‘insensible’ because the evaporation takes place from the skin constantly and it is not visible. This evaporation is an important means by which body temperature is maintained. Infants have a much greater surface are relative to body weight than do adults, and therefore, they are much more vulnerable to water loss from the skin and rapid changes in body temperature.

The water loss by visible perspiration is highly variable, ranging from zero in cool weather and when performing strenuous activities. Whenever, we loss water from perspiration, the body water is covered by eliminating a much smaller quantity in urine.


Air expired from the lungs also contains water. In any condition that would increase the rate of respiration – for example, in fever, the water loss from the lungs is much greater. Similarly, a person doing vigorous activity will loss more water from the lungs than a person who is sedentary.