A simple water target
One common rule is about 35 ml per kilogram of body weight (roughly half an ounce per pound), then a bump for heat or training. 75 kg × 35 ml is about 2.6 litres. Thirst, urine colour, illness, and medical conditions matter more than any formula. This is not medical advice.
Worked example
A simple 30 ml/kg rule at 70 kg is 2.1 litres a day, about 9 cups. Exercise, heat, and a salty meal raise that. Coffee and tea count as fluid for most people.
Thirst, urine colour, and a clinician’s advice beat a webpage. Heart or kidney conditions can mean a fluid limit. Not medical advice.
Common questions
Do coffee and tea count?
They add fluid. Plain water is still the easy default.
Can I drink too much?
Yes. Do not force gallons. Stop if you feel bloated or confused and get care.