Is Pain Like Water?

Water is what philosophers call a natural kind, that is it is a thing found in nature that has a grouping definable in terms of purely natural properties. Water isn't just related to having the chemical make-up of H2O, to be water IS to have the chemical make-up of H2O.

What about pain? Pain is certainly a real thing. It is correlated with certain things happening within the brain, but is pain nothing but those things happening within the brain? Is the brain state that causes pain the same thing as the experienced pain? Is pain a physiological phenomenon or is it something else caused by or correlated with a physiological phenomenon?