What is groundwater?

Groundwater is defined as the water that exists beneath the earth's surface, which is stored in soil and rock formations known as aquifers. This water is part of the hydrological cycle and is critical for various ecosystems and human uses, including drinking water, agriculture, and industrial processes. Groundwater is accessed through wells and springs and can be replenished through precipitation and surface water that infiltrates the ground.

In contrast, the other choices describe different aspects of water. Water that flows on the earth's surface refers to rivers, lakes, and streams, which are classified as surface water. The water contained in reservoirs is typically surface water that has been collected and stored for various purposes, such as municipal water supply or irrigation. Precipitation that seeps into the ground indicates the process of infiltration, which is part of how groundwater is recharged, but it does not define groundwater itself. Thus, the correct choice that accurately describes groundwater is the water found under the earth's surface.