How much water do you need?
A common rule of thumb is to drink about half an ounce of water per pound of body weight (roughly 33 ml per kg) each day, plus about 12 oz (350 ml) for every 30 minutes of exercise. A 160 lb person who exercises 30 minutes a day would aim for about 92 oz — roughly 11–12 cups or 2.7 litres.
Official recommendations
The U.S. National Academies set an “adequate intake” of total water — from all drinks and food — of about 3.7 litres (125 oz) a day for men and 2.7 litres (91 oz) for women. Around 20% usually comes from food like fruit, vegetables and soup, so the amount you drink is a bit lower. Needs are higher in pregnancy and especially while breastfeeding.
What counts toward hydration?
- Water is best — no calories or sugar.
- Milk, tea, coffee and sparkling water count too; moderate caffeine doesn’t cause net dehydration.
- Water-rich foods like watermelon, cucumber and oranges help.
- Limit sugary drinks and alcohol.
Signs you need more water
Thirst, dark yellow urine, headache, tiredness and dizziness can all signal dehydration. Pale yellow urine is a simple sign you’re well hydrated. Drink more in heat, at altitude, during illness with fever or vomiting, and during long workouts (consider electrolytes for sessions over an hour).
It is possible to drink too much — very large amounts in a short time can dangerously lower blood sodium. Spread your intake through the day. People with heart or kidney conditions should follow their doctor’s fluid advice.
Frequently asked questions
How much water should I drink a day?
Roughly half an ounce per pound of body weight, plus extra for exercise and heat.
Is 8 glasses of water a day enough?
It’s a reasonable starting point for many people, but needs vary with size, activity and climate.
Does coffee count as water intake?
Yes. Moderate amounts of coffee and tea still hydrate you overall.
Can you drink too much water?
Yes. Drinking very large amounts quickly can cause low blood sodium (hyponatremia).