Regular linear perspective, along with the horizon line, vanishing points, and other useful tools, is only the tip of the iceberg. What if we want to paint mountains or forests? Or the ocean? What vanishing point can there be for trees in the forest when we don't have a single line?
Anyway, there are no lines in watercolor, we only have spots of color. This is why there is another essential perspective tool - tonal balance. By the way, not only tonal, color also works in conveying perspective in watercolor!
 
This is what the final lesson from the complete watercolor course is about.
 
Don't forget to check my book about perspective: 
The Lord of Illusions: A Perspective Guide