What best defines a watershed?

• A. A drainage basin that drains water to the same place
• B. A water treatment facility
• C. A large lake
• D. A groundwater reservoir

Answer: (A)

A watershed is the land area where all the precipitation collects and drains into a single outlet, such as a river, lake, or ocean. The edges of a watershed are defined by high ground or ridges that separate it from neighboring watersheds, guiding the flow of water toward one common point. This is why the best description is a drainage basin that drains water to the same place.

The other options describe things that are not areas where runoff is collected: a water treatment facility is where water is cleaned, not where rainfall gathers; a large lake is a body of water, not the region that collects all runoff; and a groundwater reservoir is an underground storage, not the surface drainage area.