The "8 glasses a day" rule is something someone made up and it somehow spread everywhere. It has no specific scientific basis — it's a rough approximation that ignores your body weight, what you do all day, where you live, and how hot it is. For someone sitting in an air-conditioned office in Pune in December, 8 glasses might be fine. For a construction worker in Chennai in May, it's dangerously insufficient.
Let me give you a more useful way to think about this.
How to actually estimate your daily requirement
The formula most used in clinical nutrition is 35 ml per kg of body weight per day for a sedentary adult in a temperate climate. So a 70 kg person needs about 2,450 ml — just under 2.5 litres — as a baseline.
That baseline goes up significantly when you add physical activity or heat. For every hour of moderate outdoor activity, add 500–750 ml. For people living in coastal humid cities like Mumbai, Chennai, or Kochi — even without exercise — add 200–300 ml extra on hot days because you lose more water through perspiration than you realise.
A 70 kg person in an office in Hyderabad might need 2.5 litres. The same person doing construction work outdoors in June might need 4–4.5 litres. The "8 glasses" answer is the same for both — which tells you how useless it is.
The indicator that's more reliable than any calculation
Check the colour of your urine. Pale yellow (like lemonade) — you're well hydrated. Dark yellow or amber (like apple juice) — drink water now. This is more accurate than any formula because it directly reflects your body's current hydration state.
Most people wait until they feel thirsty to drink water. That's already too late — you're mildly dehydrated by the time thirst kicks in. By this point, concentration and physical performance are measurably affected. Drink before you're thirsty, especially in Indian summers.
Kidney stones — a specifically Indian concern
India has one of the highest rates of kidney stone incidence globally, particularly in what's called the "stone belt" — parts of Rajasthan, Gujarat, Maharashtra, Punjab, and Andhra Pradesh. The primary cause is concentrated urine from inadequate fluid intake, combined with diets high in oxalate-rich foods.
Urologists consistently recommend a minimum of 2.5–3 litres of fluid per day for kidney stone prevention, targeting urine output above 2 litres daily. If you've had a kidney stone once, your risk of recurrence is around 50% within 10 years — adequate hydration is the single most effective preventive measure available.
Summer heat and heatstroke
India's heat waves are getting more severe and more frequent. Heatstroke happens when your core body temperature exceeds 40°C — and dehydration is the primary risk factor. The early signs of heat exhaustion (before it becomes heatstroke) include heavy sweating, weakness, fast heartbeat, dizziness, and nausea.
On days when outdoor temperature is above 38°C, increase your water intake significantly even if you're not exercising. Don't rely on thirst. By the time you feel thirsty in extreme heat, you may have already lost significant fluid.
ORS (Oral Rehydration Salts) — available at every pharmacy in India for about ₹15–20 per sachet — is far more effective than plain water for rehydration after significant sweating or diarrhoea. The glucose in ORS helps sodium absorption, restoring electrolyte balance that plain water cannot.
Practical ways to actually hit your target
The biggest barrier isn't knowing you should drink more water — it's remembering to do it. A few things that actually work: start every morning with 500 ml before your first chai. Keep a marked 1-litre bottle on your desk. If you drink chai or coffee frequently, have a glass of water alongside each cup.
Foods count too — cucumber is 96% water, tomato is 94%, watermelon is 92%. A salad lunch in summer meaningfully contributes to your daily hydration even if you don't count it.
Can you drink too much?
Technically yes — drinking extreme amounts can dilute sodium in your blood (hyponatremia). But in practice this is essentially unheard of in normal daily life. It has occurred in endurance athletes who drink large amounts of plain water during marathons without electrolyte replacement. If you're running a marathon, that's worth knowing. For everyone else, it's not a realistic concern.
Find your personalised daily water target with our Water Intake Calculator — enter your weight, activity level, and climate to get a specific recommendation.