Dehydration is the most common cause of medical treatment following a triathlon, despite organizers providing fluids during the cycle and run legs.
Dehydration can seriously affect your physical and mental performance (even on cool days). A loss of 2% in body weight through sweating causes an increase in perceived effort, and is claimed to reduce performance by 10 to 20%. A 3 to 5% loss noticeably reduces aerobic performance and impairs reaction time, judgement, concentration and decision-making
Having access to a drink bottle during training, and carrying a drink bottle around is key to ensuring athletes meet daily fluid losses
The average adult needs to consume approximately 2.5 liters of water per day. If you are exercising, you need more water. Athletes should aim to consume a minimum of 750ml of fluid each hour.