Water is the most important element for living beings and there are organisms that can have almost 90% of their weight in water. Our body is composed of approximately 70% of water and this high value indicates the importance of this element for our organism. The water from our body can be divided into two compartments: The intracellular fluid which is the major component representing about two-thirds of body water and the extracellular fluid which can be divided into interstitial fluid (between cells) and plasma. Plasma volume represents approximately one quarter of the extracellular volume. Water is involved in several physiological mechanisms and their balance, as well as the balance of electrolytes, has major influence on its absorption and / or excretion, being regulated by precise molecular mechanisms in constant balance. If a person loses 10% of the water in his body his life can be at risk. If the lost is from 20% the health condition is so severe that can lead to death. The amount of water to be taken daily should represent at least 3% of body weight, which means the average requirement of water per person is about 2 liters per day.