What is an aquifer?

• A. A body of water found above ground
• B. An underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be extracted using a water well.
• C. An uncovered, porous layer on the surface
• D. A man-made storage tank for water

Answer: (B)

An aquifer is an underground layer of rock or loose material that can hold and transmit water. It’s permeable, so water can move through the pore spaces or fractures, and it’s deep enough that wells can tap into it to bring groundwater to the surface. Some aquifers are open to the surface with the water table right above them, while others are trapped between layers that don’t let water escape easily, which can create pressure and allow water to rise in a well without pumping. Aquifers are replenished slowly by rainfall and other sources seeping down through the soil.

That description matches the idea of an underground, water-bearing formation from which groundwater can be extracted with a well. It’s not a surface body of water like a lake, not a porous layer on the surface, and not a man-made tank.