What do we call all the land area where water drains into a common water body?

The term used to describe all the land area where water drains into a common water body is known as a watershed. A watershed encompasses not only the surface water, such as rivers, lakes, and streams but also includes all the land and soil that contributes to that body of water through precipitation, runoff, and groundwater. This area is vital for maintaining the health of freshwater systems as it influences water quality, flow patterns, and aquatic ecosystems.

While the terms basin, floodplain, and catchment are related to hydrology, they do not specifically refer to the total land area draining into a water body. A basin could denote a broader geological or topographical area, whereas a floodplain refers to the flat area adjacent to a river or stream that is prone to flooding. Catchment can sometimes refer to similar concepts, but it is typically more narrowly defined as a specific area where water is collected for a particular purpose, often in a man-made context. Thus, the precise definition and scope of a watershed make it the most accurate choice for describing the land area that drains into a common water body.