Here I’ve developed the breakaway section further, defined the gatehouses’ shapes and relationship a bit more clearly, and established the waterfall between with a kneaded eraser.
Waterfalls’ brightest highlights are usually found at the top, where the water spills over the surface and edge it’s falling from. I usually establish that edge first, then work my way downward, trying to mimic the flow and direction of the arcs and paths the water follows as it falls.
If I lighten an area too much, or a highlight needs to be moved, I’ll use a Q-Tip loaded with charcoal dust to darken the area again as needed, then reestablish highlights with an eraser. To create or adjust midtones like these, I don’t leave the Q-Tip fully loaded with dust; the result would be too dark- Much or most of the dust gets rubbed off onto scrap before I apply the remainder (carefully) to the drawing.