Where the number comes from
The calculation starts at about 35ml per kilogram of body weight — the figure most commonly cited in nutrition guidance — then adds roughly 350ml for every 30 minutes of exercise, and scales up for heat.
That weight-based starting point matters. A 50kg woman and an 85kg man have meaningfully different requirements, which the familiar "eight glasses a day" advice ignores completely. That rule appears to have come from a 1945 recommendation whose second half — that most of it comes from food — got quietly dropped somewhere along the way.
Why it matters more in India
For much of the year, across much of the country, you lose considerably more water than the standard international guidance assumes. A summer afternoon in Delhi or a humid day in Chennai can push losses well beyond what a European baseline accounts for.
Heat also increases how much sodium and potassium you lose through sweat. If you are sweating heavily for hours, plain water alone is not quite enough — nimbu pani with a pinch of salt, coconut water, or buttermilk replace what you are actually losing.
A schedule that works
Most people fail at this not through disagreement but through forgetting. Attaching water to things that already happen solves it:
- On waking — one glass, before your tea. You have gone eight hours without any.
- Before each meal — one glass. Helps with hydration and modestly with portion size.
- Mid-morning and mid-afternoon — one glass each, attached to a break you already take.
- Around exercise — one glass before, one after.
- Evening — one glass, but taper off an hour or two before bed unless you enjoy getting up at night.
A bottle you can see is worth more than any amount of intention. Keep it on the desk, not in the kitchen.
How to tell if it's working
Urine colour is the simplest check available and needs no equipment. Pale straw is the target. Dark yellow means drink more. Persistently clear usually means you can ease off.
Other signals worth noticing: afternoon headaches, dry lips, feeling tired around 3pm, and hunger that arrives surprisingly soon after eating. All of these are commonly dehydration rather than what they appear to be.
Water and weight loss
Water does not burn fat, and anyone telling you otherwise is selling something. What it does do is more mundane and genuinely useful.
Thirst and hunger signals are easily confused, so a meaningful amount of casual snacking is actually mild dehydration. A glass of water and ten minutes resolves a surprising proportion of it. Drinking before meals also reduces intake somewhat, and swapping even one sugary drink a day for water removes roughly 150 calories without any willpower at all.
If snacking is the thing you struggle with most, the weight loss tracker scores it daily alongside your walking and carbs, which makes the pattern visible quite quickly.
A note on who should check with a doctor
If you have kidney disease, heart failure, or take medication affecting fluid balance, your intake may need to be deliberately limited rather than increased. This calculator assumes general good health — please follow your doctor's guidance over it.
Frequently asked questions
How much water should I drink a day?
A reasonable starting point is about 35ml per kilogram of body weight, so roughly 2.3 litres for a 65kg woman. Add more for exercise and hot weather. The old advice to drink eight glasses regardless of your size has no particular evidence behind it.
Does tea or coffee count?
Yes. The idea that caffeine dehydrates you is largely a myth at normal intakes — the water in a cup of chai more than offsets its mild diuretic effect. Sugary drinks count for hydration too, but bring calories you probably do not want.
Does drinking water help with weight loss?
Indirectly, and more than you might expect. Thirst is often mistaken for hunger, so people snack when they are actually dehydrated. Drinking a glass before meals also modestly reduces how much you eat. Water itself burns no fat.
How do I know if I'm drinking enough?
Urine colour is the simplest guide. Pale straw means you are well hydrated; dark yellow means drink more. Completely clear generally means you are overdoing it slightly. Thirst is a reasonable but somewhat delayed signal.
Can you drink too much water?
Yes, though it is rare. Drinking several litres in a very short time can dilute blood sodium, which is dangerous. Spreading your intake across the day avoids this entirely.
Does food count towards hydration?
Around 20 percent of most people's water intake comes from food, particularly fruit, vegetables, dal, curd and soups. The target here refers to what you drink, so food is a useful buffer on top.
Medical disclaimer: this calculator gives a general estimate using standard population formulas. It is not medical advice and cannot account for your individual health, medication or body composition. Please speak to a qualified doctor or registered dietitian before making significant changes — especially if you are pregnant, breastfeeding, under 18, or managing a health condition. See the full disclaimer.