I’ve gotten pretty good water by shooting a particle-system and then overlaying it with itself several times, offset by a different number of frames. (If you can alter the playback rate for some of the strips, so much the better.) Add blur to some of the layers (but not others). Play with colors. Generally just fiddle around with it in the compositor. Lookin’ for a still shot? Just comp a series of frames down into just one. Pick the ones you like best.
Of course you do this while working with layer(s) that contain nothing but the “water.” Fatten it up in this way and lay it into the streambed. A nice sharply-specular layer in very crisp focus is sugar in the espresso.
What isn’t happening (and doesn’t have to!) is: “I mash the render button, wait X hours (again), and
.” Bzzzt… nope, not happenin’. CG is just the first step… just the source of the raw materials.