Getting water from a mage
Wondering why that Mage you asked for water yelled at you and then ignored you? Or why the Mage you were begging for a portal to Stormwind sent you all the way out to Darnassus? Briltur has the guide for you: How to ask a Mage for water.
Basically, it all boils down to "Don't be a jerk," which, frankly, is something you're either already doing, or you probably won't ever do anyway. I usually don't bug Mages for water-- it's cheap to buy, and it's not really worth the hassle. Most Mages have already had bad experiences with random people begging them for stuff, and even if you ask nicely, it isn't usually service with a smile.
The exception, of course, is instances-- if I'm in an instance with a Mage, I don't expect to be drinking my own water. Yes, I'm nice about asking for it, and yes, I'll wait if you're busy doing something else, but just as my class role as a resto Shaman is to heal when you all get hurt, your class role as a Mage is to give me water. Portals I'm not as concerned about (I've got two hearthstones, after all), but on the other hand, most Mages I'm with are happy to throw up a portal anyway, and usually do so without asking.
My guess is probably that anyone who really needs to read this guide isn't reading this site anyway, but at least you've seen it-- if you're a Mage, or see one getting pestered, now you'll know where to send the jerks.
