[rue]

Coffee etc. is still mostly water. One unit of coffee/cola/tea, compared to the same unit of water will A) give you slightly less water up front and B) cause some loss of fluid due to diuretic effect but overall you still gain fluids.

It is by far not the best source of hydration, of course. You are much better off drinking water or (preferrably unsweetened) fruit/vegetable juices - or even just eating said fruit or vegetables. Hypotonic sports drinks have their place too, but not when your exercise consists of walking up to the fridge.

[jodrellblank]

Unsweetened fruit juice is still high in sugar comparable to soda levels, and high in fructose which is particularly bad sugar to be high in.

Sugar levels in juice compared to Coca-Cola: http://www.hookedonjuice.com/

Dr Davis' Goodbye Fructose: http://heartscanblog.blogspot.com/2009/07/goodbye-fructose.h...

Dr Robert Lustig's what happens when we eat fructose and why it's bad video: http://www.youtube.com/watch?v=dBnniua6-oM

Aside from the hydration, you're probably better off with even sweetened coffee than unsweetened fruit juice.