So I got the kit earlier than I thought I would and started with it last night. I decided to go with water. 2 reasons mainly. First is that I like to keep the dust down, and even with water, as the stones dry out a little, there is some dust evident. It's minimal, but dust like that has really started to bother me lately, last 5 years or so. Second, I considered oil, but the kit warns against it. I'd probably try it anyway, but the biggest problem with oil I can see is it would make the clamp and stone holder even more slippery than they are already. Not a hassle I want to deal with, so it's water for now.