Figure 1. Typical Daily Water Inputs and Losses of a Sedentary Male

Source: Danone Nutricia Research, “Water and Hydration: Physiological Basis in Adults.� H4H Initiative (www.H4Hinitiative.com).

Drinking water and all other beverages (e.g., juices, milk, sweetened/diet/ alcoholic/hot beverages) are considered as fluids and, within this article, the sum of all these fluids will be called total fluid intake. Factors that affect the water balance are the weather and climate, clothing, diet, and length and intensity of physical activity [3,4]. Because the major source of total body water comes from fluids, it is important to consider the amount and the type of fluids you drink.

Total Water Intake Recommendations: A History Lesson The most recent recommendations concerning water intake in America were published 12 years ago [1]. There was limited data on total water intake, total fluid intake, and/or hydration for a healthy individual at population level. That is surprising, considering the first studies on human hydration were published in 1950s. In the decades following up to 2010, the number of studies increased; however, they were relevant for specific populations only (e.g., firefighters or soldiers exposed to extreme environment conditions) or 16

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specific conditions (e.g., a patient’s management in hospital or physical activity [6,7]. Moreover, because no links with the major health complications of the general population were identified, total water intake and total fluid intake were not priority research areas in nutrition. Researchers tended to focus on energy intake and nutrients coming from food rather than those from fluids. Because in 2014 there was insufficient scientific evidence indicating that a certain water intake could reduce the risk of chronic diseases, the Institute of Medicine (IOM) based its guidelines on the median water intake observed in a national survey [1]. Consequently, the reference values for total water intake of adult men and adult women (>19 years) were set at respectively 3.7 liters per day (L/day) and 2.7 L/day [1]. Knowing that foods contribute for 2030%, the more practical guidelines in the United States for adults are that men should drink 3 L/day and women 2.2 L/day [1]. Those reference values were a source of inspiration for others; China, for example, used the IOM recommendations as a reference until 2007.

Until recently, there was limited data on total water intake, total fluid intake, and/or hydration for a healthy individual at population level. In the late 2000s, researchers begin to be interested by hydration biomarkers; and methods for assessing hydration emerged [3,8]. In 2010, the European Food Safety Authority (EFSA) published the European reference values for total water intake based on a combination of observed intakes, urine osmolality values, and energy intake [2]. It was the first recommendation of water intake that included hydration biomarkers in its calculation. Currently, the EFSA guidelines for total water intake are 2.5L/day for men and 2L/ day for women, meaning that adult men