Remember the advice about drinking 8 – 8 oz glasses of water a day? Well, studies have now shown that may not be such good advice, and could actually be harmful. The study also concluded drinking caffeinated beverages has no deleterious effects on hydration either.
I had read about caffeinated beverages not causing dehydration before (from a study commissioned by the Tea Advisory Panel in the UK), so that isn’t surprising, but the debunking of the myth about drinking 8 – 8 oz glasses of water is new news to me [despite it being old news to many others].
Under some circumstances, significant fluid intake — at least eight 8-ounce glasses — is advisable: for the treatment or prevention of kidney stones, for example, as well as under special circumstances, such as performing strenuous physical activity or enduring hot weather.
In those cases I’m guessing you may need to drink even more [and it doesn't even have to be water], but the best advice now appears to be
Drink when you are thirsty, not because you believe you need to.
And stop believing everything you’ve been told! Remember, everyone has an agenda, and it most likely isn’t to benefit you.