Dehydration occurs when the body is depleted of water.
In the adult man 65% of the body's mass is made up of water. In obese men the percentage is closer to 55% and in women the respective figures are more or less 10% less than those for men.
Two thirds of the total body water is found within the cells and is called intracellular fluid, and a third is outside the cells (the extracellular fluid). A quarter of the latter is in the plasma (i.e. in the arteries, veins and capillaries) and the rest is found in between the cells (in other words outside the cells, but also outside the blood vessels). This is called the intercellular fluid.
Essential bodily processes such as circulation of the blood, excretion by the kidneys and sweating, need to be maintained and this is not possible if there is a drastic loss of fluids. Cells will dry out and malfunction.
Why we need water
Is your child dehydrated?