It is the water that makes us watercolor artists. Pigments are pigments and we can find pigments in any medium.
Surfaces have a tendency to be textured at some level, no matter what the medium.
But, it is the water that really turns us on and controls our destiny. Water is really an amazing thing. I can remember reading an article about water in Discover Magazine concerning the properties of water. It is very peculiar. It behaves differently than any other compound for example, it gets less dense when it freezes rather than more dense.