What is a human-made facility for storing water called?

A human-made facility designed specifically for the storage of water is referred to as a reservoir. Reservoirs are typically created by constructing dams or by using natural basins, allowing them to store large volumes of water for various purposes, including drinking water supply, irrigation, and flood control. They are distinguished from other water storage solutions due to their capacity and the fact that they often include additional features such as the ability to manage water levels and quality for community needs.

While tanks and water towers also serve the purpose of storing water, they differ in scale and design—tanks are usually smaller and can be underground or aboveground, while water towers typically elevate stored water to provide necessary water pressure for distribution. Wells, on the other hand, extract groundwater and are not designed for storage but rather for access to existing water sources. Hence, in the context of a human-made facility specifically for storing water, a reservoir is the most accurate term.