How much water should you drink a day?
Most adults need about 2–3 litres of fluid per day (that's the World Health Organization's number), and more when it's hot or you're moving around. A rough way to estimate it is 30–35 ml per kilogram of body weight. So a 70 kg adult lands around 2.1–2.5 litres before you add anything for exercise or a heatwave. The calculator below does the maths for you. Then the real job is sipping through the day instead of waiting until you're thirsty.
Your daily target
2.3 L
≈ 9 glasses (250 ml) · 78 oz
A general estimate for healthy adults, not medical advice. Needs vary with health, pregnancy, and medication, so check with a professional if you're unsure.
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How much water should I drink a day?
The World Health Organization puts it at roughly 2 to 3 litres of total fluid a day for most adults. A rough bodyweight estimate is about 30–35 ml per kilogram, which lands a 70 kg adult around 2.1–2.5 litres before you add anything for exercise or hot weather.
How much more water do I need in a heatwave?
You sweat out a lot more in a heatwave, so you need to top up more. Add roughly 0.5–1 litre on a hot day, sip steadily instead of waiting until you feel thirsty, and add more again if you are active or outdoors.
How much water should I drink at a desk job?
It is easy to forget at a desk, and a lot of people are mildly dehydrated by lunch, which brings on headaches and makes it harder to concentrate. Spread your daily target across the workday; a glass roughly every hour is an easy rule of thumb.
Does coffee or tea count toward my water intake?
Mostly, yes. A normal amount of coffee or tea still counts toward your fluids, even though it is a mild diuretic. Water is the better default, and very sugary or alcoholic drinks do not count the same way.