watched a prog last nite and it said no, it made no difference if you drank extra water, apart from your daily intake,i.e. coffee tea juice, they did the twins test!
i found the previous mentioned programme really interesting too - I am sure we are just told alot of rubbish but also of course everyone is so different that what helps one perhaps does not help another. I have to say if I dont drink enough water I do feel quite sluggish and shall we say can get a bit constipated but of course that wont be the same for everyone.
I thought the 2 litres a day came from a misinterpretation of a study in USA some years ago. The study result showed we need that amount of water each day and we obtain this from normal food and drink intake. However the study result was interpreted as 2 litres over and above normal intake and has been constantly repeated by health and beauty campaigns since then so people believe it.