A newborn baby can be as much as 78% water whereas a fully grown adult will be closer to 60%. In a 150 pound person, that’s over 10 gallons of water.
Regarding the capacity of the human body to consume and process water: The stomach can hold up to a gallon but the bladder must be emptied after no more than 0.2 gallons.
In the news, the claim that drinking two liters of water a day is good for us has no evidence to back it up. The boring truth is: Just drink when you're thirsty and you'll be fine. Find out more at the Belfast Telegraph.