Hydration needs change with exercise intensity due to increased fluid loss through perspiration and breathing. Higher intensity workouts lead to greater sweat production, necessitating a higher consumption of water or electrolytes to maintain optimal hydration levels. Dehydration can impair performance, reduce endurance, and increase the risk of heat-related illnesses. Athletes should monitor their hydration status before, during, and after exercise, ensuring that they adequately replenish fluids to support their body's demands based on the intensity and duration of their activities.