The water cycle is the continuous process of water moving from Earth's oceans, atmosphere and land. This cycle does not move in a particular order but in many different variations because different variables impact it like, topography, temperature and location.
Through precipitation, water condenses, forming a liquid and falling to the Earth as rain, snow, hail or fog. Once on the ground, water either remains in its liquid state, freezes, becoming ice or evaporates, or becomes a transparent gas called water vapor.
The steps of the water cycle include:
• Evaporation: Water from Earth’s surface turns into vapor from the heat of the sun and travels to the atmosphere.
• Sublimation: A process that also forms water vapor. Ice in freezing areas turns the water into vapor without the liquid phase. Varying temperatures and pressure typically cause this, the temperature must be low or the pressure high. This process takes much longer than evaporation.
• Condensation: Once the water is turned to vapor it rises into the atmosphere, the higher up it goes the cooler it gets. The cold temperatures condense the vapor into droplets that form clouds and fog.
• Precipitation: The clouds of vapor release the water after condensation. Smaller water particles combine and form drops of rain.
• Transpiration: Like evaporation, this step of the water cycle forms water vapor. Water drops are absorbed by the soil and then used by plants during photosynthesis. Plants absorb the water, using the hydrogen from the water and carbon dioxide from the air to create oxygen.
• Surface runoff: When water lands on the surface of Earth, it runs off down landscapes because of gravity, this is called runoff. This runoff water helps transport minerals and impurities. These runoff streams connect with others to form channels, returning the water to lakes, rivers and oceans.
• Infiltration: Happens when surface runoff does not return to a large body of water like a lake, river or ocean. The water is instead absorbed by the soil and becomes groundwater. The water filters through the ground and becomes pure water.
• Plant uptake: Plants need water to grow and maintain structure, they also help absorb groundwater via their root systems. The water they absorb travels to their leaves, where this water evaporates, contributing to how much water vapor is in the air.
• Evapotranspiration: Includes all processes of evaporation from the land (soil and other surfaces) and transpiration from plants.
Rainfall that stays liquid becomes runoff that forms streams and rivers. Water that is not used for some purpose eventually flows to the ocean. Water that evaporates from the ocean then condenses and eventually falls back to Earth in the form of rain. This is called the water cycle or hydrologic cycle.
There are also many places water can end up once it reaches Earth via precipitation. Each of these places has a different water cycle length.
These places include:
• Atmosphere: Water stays in the atmosphere for about 8-9 days until it is returned to Earth through precipitation.
• Ground: Water remains at the surface and stays for a month or two, or it is absorbed into the ground into shallow groundwater, not returning to the water cycle for 10,000 years.
• Snow and Glaciers: If water comes down as snow it stays on Earth’s surface for around two to six months until it melts. If this snow melts on the surface of a glacier, the glacier can hold that water for 20-100 years.
• Ocean: Water can also end up in the ocean where it can stay for more than 3,000 years.
• Ice shelf: Once water travels to an ice shelf like Antarctica the water could remain there for 900,000 years.
For a full-sized chart of the water cycle, click the image on the left.
The video below from the National Science Foundation explains each of the processes of the water cycle, where drinking water originates and how it comes to your home.
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