How Much Water Should You Drink a Day?

The "drink eight glasses of water a day" rule is easy to remember and not wrong, exactly — it is just one-size-fits-all advice for a need that varies a lot from person to person. A large, active person in a hot climate needs far more than a smaller, sedentary person in a cool one.

A better starting point: scale to your weight

A widely used estimate is about 30–35 millilitres of water per kilogram of body weight. For a 70 kg person that is roughly 2.5 litres a day — close to the eight-glasses figure, but it now scales with your size instead of ignoring it.

Add for exercise and heat

Every workout and every hot day increases what you lose through sweat. As a rough guide, add a few hundred millilitres for each block of exercise, and increase your total in hot or humid conditions. If your urine is consistently pale yellow, you are generally well hydrated; dark yellow is a sign to drink more.

• Base: about 30–35 ml per kg of body weight
• Add roughly 350 ml per 30 minutes of exercise
• Increase further in hot or humid weather

Does coffee and tea count?

Mostly, yes. Despite the old belief that caffeine dehydrates you, the fluid in coffee and tea contributes to your daily total in moderation. Water-rich foods like fruit and vegetables count too. Plain water is still the best, calorie-free choice for most of your intake.

Can you drink too much?

For healthy people it is hard to overdo it, because the kidneys handle excess easily. Drinking enormous amounts in a very short time can dilute blood sodium, but that is rare outside extreme endurance events. For everyday life, the bigger risk by far is drinking too little.

Use a weight-based estimate as your baseline, drink a bit more when you sweat, and let thirst and urine colour fine-tune the rest.