All land is part of a watershed.
We can also visualize each watershed as a catchment area divided from the next watershed by topographic features like ridgetops. The water that falls within a watershed or catchment, but isn't used by existing vegetation, will seek the lowest points ultimately, it should appear in the streams and rivers draining the system. All life depends on the soil, the water falling on that soil, and the air above and within the soil. Entire societies have disappeared because they didn't properly understand and care for their soil resource. No other resource comes close to the soil's importance.