The water cycle, or hydrologic cycle, is the continuous movement of water within the Earth and its atmosphere, driven by energy from the Sun. It involves several key processes: evaporation, where water from oceans, rivers, and lakes turns into water vapor; transpiration, where plants release water vapor through their leaves; condensation, where the vapor cools and forms clouds; precipitation, where water falls back to the surface as rain, snow, sleet, or hail; and runoff, where water flows over land, replenishing rivers, lakes, and aquifers. Water also infiltrates the soil, recharging groundwater reserves.
The water cycle is essential to life on Earth because it distributes water across the planet, supporting ecosystems and maintaining climates. It provides fresh water for drinking, agriculture, and industry while regulating temperatures through processes like evaporation and precipitation. This cycle sustains habitats for countless species, connects terrestrial, aquatic, and atmospheric environments, and ensures the availability of water, a fundamental resource for all living organisms.