Why fluid needs climb with activity
Total daily water need is dominated by how much is lost, and sweat loss rises sharply with exercise volume, intensity, and heat. The diagram steps from sedentary needs of roughly 2 L per day up through moderate exercise, endurance training, and ultra-endurance loads that can exceed 6 L per day in demanding conditions.
These figures include water from all sources, including food, not just what is drunk. They are population guides, not precise targets, because body size, climate, and individual sweat rates vary widely.
Reading the tiers without overdrinking
The higher tiers apply to people doing substantial training, not to a sedentary person who simply drinks more. Both under-drinking and excessive overdrinking carry risk, and overhydration during long events can dangerously dilute blood sodium, a condition called hyponatremia.
This is general educational information, not medical advice. Thirst, urine color, and body-mass change before and after sessions are practical cues, but anyone with kidney, heart, or other conditions affecting fluid balance should set targets with a qualified professional.