Caffeine

I suspect the caffeinated beverage does not absorb into your body but just passes through without hydrating you.

I'll answer to the best of my knowledge.

Caffeine in itself does not cause dehydration. It causes you to urinate more than usual. If you drink a caffeinated bev. in moderation along with the healthy amount of non-caf fluids (in particular water); you probably will not become dehydrated.
Caffeine does a lot more though than simply being a diuretic. It causes psychomotor arousal (amongst other things). Your heart beats faster, you breathe faster, and the blood is pumping through your body quicker. This uses water! and energy.
So, if you were to simply drink caf beverages, you run the risk of dehydration because you have heightened the use of water in your body and your body can not return to a normal level of use until you stop consuming so much caffeine! A body in constant arousal is a body that quickly becomes dehydrated.

That's what I think, anyways.

flushd-

Thank you.

It is frightening. I have been drinking Diet Coke (caffeinated) as just about my only source of liquids for at least 20 years.

Whoa, you really love Diet Coke, eh?

Here....have a bottle of water. You might hate it for the first while, but I bet you'll feel better. Believe me, you get used to the 'non-taste' of water.

And OMG; you are most likely caffeine dependent too. Cut back slowly on the DC so you don't get the headaches, tummy pains, and other fun stuff too badly.

Guzzle that water my friend!

A FRIEND OF MINE SAYS IN THIS HOT(UK) WEATHER,PEOPLE WITH HEART CONDITIONS SHOULDN'T DRINK MORE THAN 2 CANS/DRINKS OF CAFFEINE![/size][/b]

And the rest of us should???