Do not wait until you are thirsty to drink while running, as thirst is a signal that dehydration has already set in; instead, plan for regular hydration of 300 to 500 ml of water per hour from the start of your exercise.

noli's read

The advice to aim for 300 to 500 ml of water per hour is highly consistent and aligns with the recommendations of the American College of Sports Medicine (ACSM), which suggests personalized hydration to prevent a body weight loss of greater than 2% during exercise. However, the claim that thirst indicates it is 'already too late' is scientifically nuanced today. A significant meta-analysis conducted by researcher Eric Goulet demonstrated that drinking only according to the sensation of thirst (known as ad libitum hydration) proves largely sufficient to maintain optimal endurance performance during moderate efforts. Thirst is not a late failure signal, but an extremely precise biological regulatory mechanism. While planning water intake remains useful over very long distances to anticipate fatigue, trusting one's thirst remains a safe and validated strategy for the majority of athletes.

the sources

1. 1Valtin H 2002