The fabled city of Xavian lies nestled deep within eastern Ashenvale, and tales of its ancient knowledge are well known among the learned. It is said that the waters of Xavian hold vast magical powers.
I would have a sample of those waters, from their source.
Take this flask and go to Xavian. Gather water from the bottom of its highest waterfall, and return to me. And use care as you move through that ancient city--satyrs now hold the ruins and do not like mages prying into their affairs.
Follow the river north, a bit east, of Splintertree Post, just northwest of Satyrnaar. Two rivers meet - follow them north past the lake until you hit the waterfall. Try not to go too far east into Satyrnaar or you may get mobbed. Just take the river - only a few level 25 swamp beasts.