Evaporation, condensation, precipitation, runoff, infiltration, groundwater, ice, rivers, oceans, watersheds, climate, and human water use
The water cycle
The water cycle, also called the hydrologic cycle, is the continuous movement and storage of water through the atmosphere, oceans, land, ice, groundwater, rivers, living things, and human-built systems.
What the water cycle is
The water cycle describes where water is stored on Earth and how it moves between those places. Water can be liquid, solid, or gas. It may be in oceans, clouds, rain, snow, glaciers, rivers, lakes, soils, aquifers, plants, animals, and human systems. The cycle has no single starting point because water is always moving, changing state, or being stored for different lengths of time.
Evaporation and transpiration
Solar energy warms water at the surface of oceans, lakes, rivers, soils, and plants. Some liquid water becomes water vapor through evaporation. Plants also release water vapor through transpiration. Together, evaporation and transpiration move water from land and surface water into the atmosphere, where winds can carry it far from where it began.
Condensation and precipitation
As moist air rises or cools, water vapor can condense into tiny droplets or ice crystals, forming clouds, fog, or dew. When droplets or crystals grow heavy enough, water returns to the surface as precipitation. Precipitation can fall as rain, snow, sleet, hail, or freezing rain, depending on temperature and atmospheric conditions.
Runoff, rivers, and oceans
Some precipitation flows across the land as runoff, especially when soil is saturated, frozen, paved, steep, or unable to absorb water quickly. Runoff gathers in streams and rivers, often moving through watersheds toward lakes, wetlands, estuaries, and oceans. Rivers are visible pathways in the water cycle, but they are only one part of a much larger system.
Infiltration and groundwater
Some water soaks into the ground through infiltration. It may stay near the surface as soil moisture, be taken up by plant roots, or move deeper to recharge groundwater stored in aquifers. Groundwater can flow slowly for days, years, centuries, or longer before emerging into springs, streams, wetlands, wells, or the ocean.
Ice, snow, and storage
Water can be stored for long periods in glaciers, ice sheets, snowpack, lakes, deep groundwater, and the ocean. Seasonal snowpack is especially important in many regions because it stores winter precipitation and releases meltwater in warmer months. Changes in ice and snow affect river flow, water supply, sea level, and ecosystems.
People and the modern cycle
Human activity is now part of the water cycle. Cities speed runoff through pavement and storm drains. Farms move water through irrigation and drainage. Dams store and release river water. Wells withdraw groundwater. Land clearing changes evaporation and infiltration. Pollution affects water quality, and climate change alters evaporation, precipitation, snow, droughts, floods, and extremes.
Why it matters
The water cycle matters because it connects weather, climate, drinking water, farming, floods, droughts, ecosystems, energy, cities, and oceans. Understanding it helps people manage water as a moving system rather than a fixed supply. Every watershed decision, from paving land to pumping groundwater, changes how water moves and who can use it later.