What is an aquifer?

An aquifer is defined as an underground formation that contains groundwater. It consists of permeable rock or sediment that can transmit water, allowing it to store and deliver groundwater to wells and springs. Aquifers play a crucial role in the hydrological cycle by providing a source of water for drinking, agriculture, and industrial use.

In the context of the options provided, the definition of maintaining and storing groundwater clearly aligns with the concept of aquifers. This formation helps in the movement and storage of water that infiltrates the ground, making it vital for water supply and ecosystem health. The other options describe various aspects of water sources, but they do not encapsulate the specific geological characteristics and functions that define what an aquifer truly is.