Which cycle is primarily responsible for replenishing Earth's surface water?

• A. Nitrogen cycle.
• B. Sulfur cycle.
• C. Water cycle.
• D. Carbon cycle.

Answer: (C)

Water continually moves between the atmosphere, land, and bodies of water, keeping surface water replenished. Evaporation from oceans and other water bodies lifts water into the air, where it cools and condenses into clouds. When conditions are right, precipitation returns water to the surface as rain or snow, feeding rivers, lakes, and wetlands. Some of this water also infiltrates the soil and groundwater, which then reconnects with surface water through springs and baseflow, or later surfaces as runoff into streams and lakes. Solar energy powers evaporation, and gravity drives precipitation and runoff, making this cycle the primary mechanism that maintains surface water supplies over time.

Other cycles involve different elements—like nitrogen, sulfur, and carbon—and describe how those elements move through ecosystems and Earth's materials. They influence water quality and availability indirectly, but they do not primarily replenish surface water in the same way the water cycle does.