IMO you want to use water either way. I don't like to use butter myself, I use coconut oil. You really can't regulate the temps well without water, but with it there is a nice buffer and it puts your temps in the ideal range without even having to think about it. I like to use leaf for oil, because what else am I going to do with it? I'll use around a pound of leaf to 16 oz of oil, and use a gallon or so of water as a buffer. It's like turning garbage into gold.