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Water, accounting on average for 60% of the body weight, is the largest component of the human body. It is essential to life and we cannot live more than a few days without water.


Water has indeed numerous functions in the body: it is the building material for cells and body fluids; it acts as a reaction medium, as a solvent and as a reactant. It is also the transporter of nutrients and helps in the elimination of body wastes through urine. It is essential for the control of body temperature through sweat evaporation.


The aim of the document is to review the current scientific evidence on hydration physiology, with a focus on adults, as being representative of the majority of the population. It details the water content, absorption and distribution in the human body, reviews the sources of fluid losses and water inputs and the regulation of body water balance. It finally gives overview of the main recommendations for daily water intake.

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