Fill the Empty Blue Waterskin at the Ruins of Stardust in Ashenvale and return to Brine in the Barrens.
Take this waterskin and head deep into the lush forest the night elves call Ashenvale. It is to the far north of the Barrens.
Once you've entered the forest, travel west. Along the mountains that separate Stonetalon and Ashenvale, and beyond Lake Mystral, you will find a holy place: the Ruins of Stardust. At the center of the lake you will find a small fountain.
Bring me a sample of the fountain's water. It will be the final component you'll need before I send you back to Islen.