Quick Water Question

[Scythe13]

Okay, this is something I've still not figured out yet.

Where is everyone getting their water use per person stats from?

I hear things like 2 Litres of water per person per day, just for drinking.

I've not read a single research project showing evidence for people to drink that much water. The best I've come across was based on no research at all, just a woman talking about drinking 1ml of water per calorie you consume. But her recommendation was not based on any scientific research!

Answers please.