Well, according to www.snopes.com, the 2L per day minimum is an urban legend:

http://www.snopes.com/toxins/water.htm

Dr. Barbara Rolls, one of the co-authors of "Thirst (Problems in the Behavioural Sciences)", and Holder of Guthrie Chair in Nutrition and Professor of Biobehavioral Health at U Penn, says she has no idea where the number came from, and most experts agree it's much too high. In fact, some experts maintain (though they advise against it) that most people take in enough water through solid food that they could survive without drinking any liquids at all.

Studies have also shown that drinking coffee, cola, etc. does NOT dehydrate you, so you don't need an extra hit of water to compensate for that double latte.

Snopes traces the "well-known facts" to a self-published book by an Iranian-born doctor living in the USA who did no independent research and sounds like a classic quack/crackpot to me.

Obviously, in hot dry surroundings, or where you're doing a lot of physical work (e.g. hiking with a heavy backpack on a hot summer day) you're going to go through more water than sitting in an air-conditioned office. But for most purposes, 1 litre a day is quite sufficient.