The “eight glasses” rule was never designed for 42°C afternoons. Your actual need varies with heat, activity and what you eat — here is a practical guide.
A better baseline
Take your weight in kilograms and multiply by 35 ml for a moderate day. A 70 kg adult lands near 2.5 litres — before accounting for sweat losses, which can add another litre on hot commutes.
Signs you are behind
Dark urine, afternoon headaches, and fatigue that lifts after a glass of water. Thirst itself lags; by the time you feel it you are already mildly dehydrated.
Beyond plain water
Lassi, nimbu pani with a pinch of salt, and water-rich fruits (watermelon, cucumber) all count. Limit strong tea rounds in peak heat — caffeine is mildly diuretic in large doses.
The office trick
Keep a marked 1.5-litre bottle at your desk and finish it by day’s end. Measurement beats intention every single time.
