My understanding is that the dehydrating effect of coffee is somewhat overstated, especially for people who are regular drinkers. Last time they updated the "drink x cups of water a day" they included coffee as part of that fluid intake.

Though I've found that trying to get all your fluids from coffee isn't healthy, any more than trying to get them all from beer.... fun, but not sustainable.

That's probably true--I haven't read any recent data.

Still, I remain convinced that a physical body that evolved upon the theory of water intake will be healthier if you, you know, drink water.