A water pan stabilizes temperature fluctuations acting like a heat sink, catches drippings, and provides a moist environment for my meat. I believe moisture in meat is closely related to the amount of fat rendered. That being said, I have used a pizza pan and my trusty Costco foil pan with water, and both turned out great Que. I like the foil water pan because the drippings don't burn. Can't go wrong really. Love Kamado kooking.
Char-Griller Akorn , Maverick ET-732 , Red Thermapen Backlit