HOW MUCH WATER SHOULD YOU DRINK DAILY? By Roselyne Y. Wagner, PhD, and Isabelle Guelinckx, PhD
Global recommendations on water intake vary between health authorities. What is the scientific evidence behind them? Water is essential for life. Humans can live for weeks without eating but only a few days without drinking. Yet, most people are not aware of the existing daily recommendations for fluid intake. As drinking is so important for health, why aren’t we more aware about how much we need to drink every day?
We Are What We Drink The human body is composed of approximately 60% water, depending on age, sex, and climate conditions [1,2]. Because water is involved in numerous biological functions in the body—such as building materials for cells and fluids, and temperature control—the body tightly regulates the amount of total body water. It is constantly balancing water losses and water gains. Every day, the body loses water through sweat, respiration, fecal losses, and urine, and it also gains water from metabolic reactions, food, and fluids. (See Figure 1 on p.16.) Metabolic water production is very limited: it represents, on average, only 300ml. The largest gain of water is from dietary intake: it’s estimated that approximately 20% of total water intake comes from food (moisture), and 80% from fluids .