Vatten

In the Human Body

Water is a basic component of all living organisms. The quantity of water present in a human adult is equal to about 60% of total body weight with relative variations according to age and sex. At birth the ratio rises to an approximate 75%. The absence of water is more life threatening within a shorter period of time than solid food fasting. A loss of 10% of the total water content in an organism results in the inability to perform organized physical activity.

Whether it is a free molecule or bound to others, water has various biological functions:

	It takes an active part in digestion by facilitating transportation and solubility of chemicals through the gastrointestinal tract until the soluble nutrients passing through the intestinal wall can be absorbed by blood and lymph vessels and diffuse into body cells.
	It is the medium through which metabolic reactions take place. Blood, for example, contains about 92% water and carries catabolic residues from the cells to the organs of the excretory system: kidneys, lungs, skin .
	Water allows for the passage of substances from the cells to the intercellular spaces, to blood vessels and vice versa.
	It helps regulate body temperature through perspiration and the elimination of water vapour through the lungs.

The presence of water in the body can be divided in two large categories of function: intercellular which comprises about 50% of total body weight and extracellular which corresponds to 20% of total body weight of which 5% is water from blood and 15% is interstitial water.

Exogenus and endogenous water: the need for water

The greatest portion of water in the human organism derives from exogenous sources. It is therefore introduced into the body through the intake of food and drinks. The remaining portion has an endogenous origin and is formed as a final catabolic product in the oxide-reduced processes.

An individual is considered balanced in terms of water content when his/her water intake together with the amount that is formed within the body is equivalent to the quantity of eliminated water (urine, lung and skin's excretory functions ).

The need for water isn't the same for all. It instead varies with age and, in fact, an infant must consume proportionally more water than an adult due to a relatively higher rate of metabolism and perspiration rate / body surface area.

Regarding adults, a recommended water consumption is one which is directly proportional to the sum of calories comprised in a daily diet, i.e. a ratio equivalent to about 1ml of water per calorie. For a child, the suggested intake is 1,5ml water/calorie.