About 56% of the body of an adult man is a liquid. The major part is in cells, and about one third is outside the cells.

The fluid is constantly moving around the body, so maintaining a relatively constant volume and constant composition of body fluids is essential for the homeostasis of the organism. This constant is special because there is a continuous exchange of liquids and solutes with both the external environment and the various sections of the body. For example, intake water that is highly variable must be carefully adjusted to equal the excretion of water from the body to prevent the increase or decrease in volume of body fluid.

Water entering the body comes from two main sources:

  • it is taken in the form of beverages or water in the food, which normally adds about 2100ml / day to body fluids;
  • Another source is the fluid that is synthesized in the body as a result of oxidation of carbohydrates, which is about 200ml / day.

This ensures a total required daily water intake of about 2300ml / day. The intake of a liquid is very different among individuals, even when it comes to one person, the amount varies by day, depending on the climate, habit, and degree of physical activity.

The daily intake of water that is necessary for the proper functioning of the body is 2 – 3 liters / day.

This quantity as well as the need for water intake has increased after some physical activity, at elevated external temperatures, in some diseases. The reason for the increased need is the increased water loss. Normally, water is lost through the kidneys (urination) in an amount of about 1400ml / day. It’s a normal diuretic. The volume of urine can be reduced by up to 500ml (for dehydrated person), or increased. Another way of losing the fluid is through the feces, where only 100ml / day is lost. This can be increased to a few liters a day for people with a strong diarrhea. Therefore, strong diarrhea can be life-threatening if it is not treated within a few days. A significant way of losing the fluid is through sweating. This amount of fluid that is lost in this way is variable and is directly dependent on physical load and external temperature. Thus, the amount of water extracted can be from 100ml / day to 1-2 liter / hour. The insoluble loss of fluid that is constantly taking place is both evaporation from the respiratory tract and diffusion through the skin. Under normal conditions this is about 700ml. Pathological fluid losses are seen in diseases such as: increased metabolism and fever, diarrhea, renal impairment, burns, stress, injuries, bleeding, parathyroid gland disease, chemotherapy of malignant diseases, hypervitaminosis.

If water and electrolyte losses are not compensated, there will be serious dehydration with consequences within a few days. Each patient is a special problem. Individual clinical status is the main and only guideline that determines how to recover the lost fluid.

dr Jelena Mišović