Of course, this varies from person to person, but roughly 2 liters (34 oz) per day is a good goal. To be more precise this formula will help you to calculate the exact amount: Water (in liters) to drink during the day = your bodyweight (in Kg) x 0,033 Or in lbs Water (in ounces) to drink during the day = your bodyweight (in lbs) x 0,5