Daily water intake requirements vary significantly based on body weight, activity level, climate, and individual physiology. The widely quoted "8 glasses a day" rule has no strong scientific basis — actual needs are highly individual. The most evidence-backed approach is weight-based: approximately 35ml per kg of body weight for adult males and 31ml/kg for females at baseline.

For athletes and active individuals, this baseline needs to be increased based on sweat loss. A one-hour moderate training session in temperate conditions adds approximately 600–900ml of water loss through sweat. In hot and humid Indian summers, this can exceed 1.5–2 litres per hour during intensive outdoor sport.

The colour of your urine is one of the most practical hydration markers: pale straw yellow indicates good hydration, dark yellow or amber indicates dehydration. Thirst is also a reliable indicator for most healthy adults — but athletes should drink proactively before feeling thirsty during long sessions.