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“Drink eight glasses of water a day” is one of the most repeated health tips. It’s a reasonable rough guide — but your real needs depend on your body, your activity and where you live. A construction worker in a Chennai summer needs far more water than an office worker in a cool, air-conditioned room.
This article is general information, not medical advice. People with kidney, heart or liver conditions, and pregnant or breastfeeding women, should follow their doctor's guidance on fluids.
A simple way to estimate
A widely used rule of thumb:
Base need ≈ 35 ml × body weight (kg)
Then add:
- About 350 ml for every 30 minutes of exercise
- About 500 ml extra in hot or humid weather
Example 1: 65 kg, 30 minutes of exercise, mild weather → 2,275 + 350 = about 2.6 litres (around 11 glasses of 250 ml).
Example 2: 80 kg, 60 minutes of exercise, hot climate → 2,800 + 700 + 500 = about 4 litres.
Food counts too
Not all your water comes from glasses of water. Fruit and vegetables (watermelon, cucumber, oranges), dal, curd, buttermilk, soups, milk, tea and coconut water all contribute. On average, food provides a meaningful share of daily fluids.
Signs you need more water
- Dark yellow urine — aim for pale straw colour
- Thirst and a dry mouth
- Headache, tiredness or difficulty concentrating
- Dizziness, especially when standing up or after exercise
- Muscle cramps during exercise or in the heat
Older adults often feel less thirsty even when they need water, so regular drinking habits matter more as we age.
When you need extra
- Hot weather and heatwaves — sweat losses rise sharply
- Exercise and physical work — drink before, during and after
- Fever, vomiting or diarrhoea — oral rehydration solution (ORS) helps replace both water and salts
- Pregnancy and breastfeeding — needs increase (follow your doctor’s advice)
- Air travel and air-conditioned offices — dry air increases losses
Easy habits to stay hydrated
- Start the day with a glass of water.
- Keep a bottle at your desk — you’ll drink more if it’s in sight.
- Drink with every meal.
- Set gentle reminders on your phone if you often forget.
- Choose water over sugary drinks — soft drinks and packaged juices add lots of sugar.
Calculate your daily goal
Our Water Intake Calculator estimates your daily water needs from your body weight, exercise and climate, and shows the result in litres, glasses and one-litre bottles.
Free toolTry the Water Intake CalculatorEstimate how much water your body needs each day.Frequently asked questions
Do tea and coffee count towards water intake?
Yes. Although caffeine has a mild diuretic effect, moderate amounts of tea and coffee still add to your total fluid intake.
Should I drink more water in winter?
You may feel less thirsty in winter, but you still lose water through breathing and dry indoor air. Keep drinking regularly.
Is it possible to drink too much water?
Yes. Drinking very large amounts quickly can dangerously dilute sodium in the blood. Spread your intake across the day and follow medical advice if you have kidney, heart or liver conditions.
For general information only — not medical advice, diagnosis or treatment. Always consult a qualified doctor, pharmacist or healthcare professional. Written by the Toolsopedia team. Spotted an error? Tell us and we’ll fix it.