I've been thinking about water intake recently, I drink 4 litres of mineral water during my working day, top this up with breakfast juice,coffee and a couple of pints of diluting orange I reckon I drink over 5 litres of liquid a day. There is no way that I need to drink this much, I couldn't possibly need to replace this amount of liquid.
I notice I drink way more than most people I know. On a recent visit to Canada, I took a fishing trip, the guide picked me up from the hotel at 7.00am and during the course of the day, until 7.00pm, he drank 2 huge cups of coffee. We were trekking over rough terrain and I couln't believe someone could survive on this intake of caffeine, which I always thought caused dehydration..this appears to be untrue:

Regular coffee and tea drinkers become accustomed to caffeine and lose little, if any, fluid. In a study published in the October issue of the Journal of the American College of Nutrition, researchers at the Center for Human Nutrition in Omaha measured how different combinations of water, coffee and caffeinated sodas affected the hydration status of 18 healthy adults who drink caffeinated beverages routinely.
"We found no significant differences at all," says nutritionist Ann Grandjean, the study's lead author. "The purpose of the study was to find out if caffeine is dehydrating in healthy people who are drinking normal amounts of it. It is not."

The same goes for tea, juice, milk and caffeinated sodas: One glass provides about the same amount of hydrating fluid as a glass of water. The only common drinks that produce a net loss of fluids are those containing alcohol — and usually it takes more than one of those to cause noticeable dehydration, doctors say.

I often think what someone 50 years ago would think of our habits today, spending a quid on a litre of water from a vending machine and always needing to have a bottle somewhere nerby. It's all a myth after all, even the 8 glasses of water a day:
http://www.snopes.com/toxins/water.htm