Abstract: This review aims to investigate the physiological mechanisms that underlie the hydro-electrolyte balance of the human body and the most appropriate hydration modalities for individuals involved in physical and sports activities, with a focus on ultra-endurance events. The role of effective hydration in achieving optimal sports performance is also investigated. An adequate pre-hydration is essential to perform physical and sporting activity in a condition of eu-hydration and to mantain physiologic levels of plasma electrolyte. To achieve these goals, athletes need to consume adequate drinks together with consuming meals and fluids, in order to provide an adequate absorption of the ingested fluids and the expulsion of those in excess through diuresis. Therefore, there are important differences between individuals in terms of sweating rates, the amount of electrolytes loss and the specific request of the discipline practiced and the sporting event to pursue.