Mine is one you stand on, so that takes surface out of the equation. An interesting point if I'm remembering correctly is that tap water is a conductor because of the minerals in it. Pure water is an insulator. I'm not quite sure though what constitutes pure water (perhaps what they call de-ionized water). I would assume that as long as you're using the data for trending, doing it the same way, on the same surface at the same time of day would be best.
I know that I get more consistency if I do (as the manufacturer suggests) late afternoon measurements. The problem with that is I forget. At the moment I'm not really trending bodyfat information. I probably should be, it's just that I'm not.
