What is meant when a spice is water-soluble? Coriander and basil are said to be water-soluble. However, I'm not quite sure what this means.  If you put the leaves into water the leaves do not dissolve. They are still there at the end.

I know certain nutrients can be water soluble — e.g., vitamin C — but what is meant by a spice?
"Water soluble" vs. "fat soluble" refer to the flavor of the spice, rather than the physical leaves, seeds, or grains.  That is, if you put a bunch of basil leaves (especially dried ones) in a glass of warm water, and leave it for a few minutes, the water will continue to taste like basil even after you've strained out the leaves.  With fat soluble spices like whole cumin seeds, you generally need to "bloom" them in hot fat (like butter or vegetable oil) for their flavors to spread.  As a rule, all spices are fat-soluble but some are water-soluble as well.

Of course, in reality almost all spices are both water and fat soluble to some degree.  It's just that some spices spread their flavor much better in fat that in water.