Why is groundwater from an aquifer often cleaner than surface water?

• A. because pollutants are filtered by rock and soil deep within Earth
• B. because it forms where fresh and salt water meet
• C. because it rises to the surface near the ocean
• D. because it receives water directly from precipitation

Answer: (A)

Groundwater from an aquifer is often cleaner because water must pass through layers of rock and soil that act as natural filters. As water moves downward, particles are trapped and dissolved substances can adhere to mineral surfaces, reducing pollutants that reach the aquifer. In contrast, surface water is exposed to runoff, sediments, chemicals, and microbes from land and human activity, which can make it dirtier.