What is an aquifer?

• A. A cloud of water droplets in the sky
• B. The process of water evaporation
• C. An underground water reservoir
• D. A large surface water body

Answer: (C)

An aquifer is an underground layer of rock, sand, or other material that holds and transmits groundwater, acting like a natural underground reservoir. Water moves slowly through the porous material and can be accessed by wells or natural springs. This is different from a cloud in the sky, which is formed by condensation, or from evaporation, which is the change of liquid water to vapor. It’s also not a large surface body like a lake or river. Recharge happens when rain or surface water infiltrates down to refill the underground store, and aquifers can be confined by impermeable layers or be open to the surface if they are unconfined.