This was a demonstration painting for one of my two-day workshops. The visual clues most effective in describing water are reflections. However when the water surface is broken, there are no reflections. So a rushing river causes a few problems for the watercolorist.
The basic rule of thumb in painting water is to find a place to include reflections. Even in moving water, you should find a place where the water is still enough to include a hint of reflections as in the center of this painting where I could include some verticals from the river birches.
It is necessary to get the darks in the background foliage so I know what my reflections will look like. With the darks in place on the right I can move on and finish the water. I use the same technique on the distant trees on the left side as well.
Notice both the areas where negative painting was used. As I move to the foreground, details were added such as leaves at right and small ripples around the foreground boulder. These little touches should be reserved for the final stages and should not be overdone.