In endurance sports (and most other sports), getting your hydration just right is important. Dehydration is common and may cause performance to suffer. Overhydration, although less common, can be a much more serious issue. Knowing how to hydrate properly will help you achieve peak performance and avoid serious risks.
The goal of drinking during exercise is to prevent significant dehydration and to enable peak performance. It’s your sweat rate that determines your fluid requirements during exercise whether you are running a marathon, competing in long distance triathlon or playing a game of basketball or soccer.