How much water should you actually drink a day?

Where does the 35ml per kg baseline come from?

It's a commonly cited general hydration guideline for healthy adults — roughly 35ml of water per kilogram of body weight per day, before accounting for exercise, climate, or individual health factors. It's a reasonable starting estimate, not a clinically precise requirement; actual needs vary by individual, and this figure includes water from all sources, not just plain drinking water.

Does this include water from food and other drinks?

The baseline figure represents total daily water needs from all sources combined, including food — fruits and vegetables in particular are often 80-95% water — and other beverages, not just plain water you deliberately drink. Most people get roughly 20% of total water intake from food, so the number shown here is a reasonable target for total fluid intake, not a mandate to drink that exact amount as plain water alone.

Should I drink more if I have a medical condition?

This is a general wellness estimate, not medical guidance — certain conditions (kidney disease, heart failure, and others) require fluid intake to be managed specifically by a doctor, sometimes with a lower limit than a general calculator would suggest. If you have a relevant medical condition or take medication affecting fluid balance, follow your doctor's specific guidance over this general estimate.

Worked example: a 70kg person exercising 30 minutes a day in a hot climate: base need is 2,450ml (70 × 35ml), plus 350ml for exercise, plus 245ml (10%) for hot climate — a daily target of about 3,045ml, or roughly 3 liters.