Water in an Indian summer
The eight-glasses rule has no research behind it. A weight-based estimate is better, and your own thirst is better still.
A better starting estimate
A common clinical estimate is 30–35 ml of total fluid per kg of body weight per day. For a 60 kg adult that is 1.8–2.1 litres; for an 80 kg adult, 2.4–2.8. European reference values land in the same neighbourhood, at roughly 2.0 litres a day of total water for women and 2.5 for men under temperate conditions.
The word doing the work in all of those figures is total. Roughly 20–30% of it normally arrives as food — dal, sabzi, curd, dahi, fruit, and the chai nobody counts. The number you need to drink is meaningfully lower than the number you need to consume. Full weight-by-weight figures are on the water intake calculator.
Where "eight glasses" came from
A 1945 US recommendation suggested about 2.5 litres of water a day for adults — and, in a sentence almost universally dropped when quoted, noted that most of that is contained in prepared food. The surviving fragment became "drink eight glasses of water," which is a plausible-enough target and has never had trial evidence behind it as a threshold.
What heat actually changes
Sweat rates vary enormously — from a few hundred millilitres an hour in mild conditions to well over a litre an hour for someone working or training in 40 °C heat with high humidity. Humidity matters as much as temperature, because sweat that does not evaporate does not cool you and you simply lose more of it. A Chennai afternoon and a Delhi afternoon at the same temperature are not the same hydration problem.
Practical adjustment: add roughly 500 ml to 1 litre on hot days, and more if you are outdoors or physically working. If you are sweating heavily for hours, plain water alone eventually becomes insufficient — you are losing sodium too, which is what nimbu-pani with salt, chaas and ORS are for.
| Body weight | Temperate | Hot day | Outdoor work or training in heat |
|---|---|---|---|
| 50 kg | 1.5 – 1.8 L | 2.0 – 2.5 L | 3.0 L + |
| 70 kg | 2.1 – 2.5 L | 2.6 – 3.2 L | 4.0 L + |
| 90 kg | 2.7 – 3.2 L | 3.2 – 4.0 L | 4.5 L + |
Total fluid including that obtained from food. These are planning estimates, not requirements — individual sweat rates differ by a factor of three or more.
The test that beats every formula
Urine colour. Pale straw means you are fine; dark yellow means drink more; completely colourless all day usually means you are drinking more than you need. Thirst is a reasonably good signal for healthy adults under normal conditions — it becomes less reliable in older adults, during intense exercise, and in extreme heat, which are precisely the situations where deliberate drinking matters.
Questions
How much water should I drink a day in India?
A reasonable estimate is 30–35 ml per kg of body weight of total fluid — roughly 2.1–2.5 litres for a 70 kg adult — with 500 ml to 1 litre added on hot days and considerably more for outdoor work or training in heat. Around 20–30% of total fluid normally comes from food.
Is 8 glasses of water a day correct?
It is a rough approximation with no trial evidence behind it. The figure traces back to a 1945 recommendation of about 2.5 litres a day which explicitly noted that most of that comes from food — a clause that was dropped as the advice was repeated.
How do I know if I am drinking enough water?
Urine colour is the simplest reliable check: pale straw is fine, dark yellow means drink more. Thirst is a reasonable guide for healthy adults in normal conditions, but it becomes less reliable in older adults, during intense exercise and in extreme heat.
More guides
General information only — not medical advice. These calculators use published population formulas; they cannot account for your individual health. Consult a doctor before major diet or exercise changes. See data & method for every formula and citation used on this site.