Water is constantly on the move through the ocean, land, in the atmosphere, and underground, and is essential for life  on earth. It is recycled over and over through a process known as the water cycle. During this cycle, water changes state between solids (ice), liquids (water), and gases (water vapor). The rain that you see falling from the sky could have been water in the ocean only days beforehand.

In the atmosphere, water vapor rises and cools which forms water droplets through a process known as condensation. Condensation is the process in which water changes from its state of a gas or vapor into a liquid. These tiny water droplets combine to form clouds. Once the droplets become too heavy to stay in the air, they begin to fall to the ground in the form of rain, snow, or other forms of precipitation. A large majority of the precipitation that falls become a part of an ocean, river, lake, or stream. Snow and ice that falls to Earth may lay on its surface within glaciers or other forms of ice. Some precipitation seeps into the ground to become groundwater. The length of time in which water spends in each phase of the water cycle varies. A drop of water may spend several thousand years in the ocean before transferring to the next phase of the water cycle, while a drop of water spends an average of eight days in the atmosphere before falling to Earth.

Water's state, whether it be a solid, liquid, or gas, is generally determined by temperature. Water continuously changes states, but the amount of water on Earth remains the same.

Water is an important part of life on this planet, covering more than three-fourths of the Earth's surface. Learn more about the water cycle that provides us with water to drink, food to eat, and sufficient weather patterns required to successfully grow crops.

  • Water-Cycle Diagrams and Summaries: Explore the water cycle through a diagram or summaries of the various processes involved.
  • The Hydrologic Cycle: Learn how water is distributed among the oceans, land, and the atmosphere through the water cycle.
  • Flash Water Cycle: Interactive flash video used to walk students through each step of the water cycle.
  • Water Cycle Animated Diagram: This Earth-Guide provides an interactive diagram of how water changes states, how it moves, and where it exists.
  • Interactive Water Cycle: Information about the continuous process involved in the water cycle and how clouds form through condensation.
  • NASA and the Water Cycle: Article providing details on the water cycle, as well as a chart with the estimates of global water distribution on Earth.
  • Water Cycle Lesson: Interactive lesson and video of how the water cycle works and information on each step of the complex process. 
  • Introduction to the Water Cycle: Summary of each step of the water cycle, including evaporation, transpiration, condensation, precipitation, and run-off.
  • Weather and Climate Basics: Details of the recycling motion of the water cycle and how it moves from the atmosphere to underground.
  • Cycle with Water: Students can use the navigation buttons to review the primary stages of the water cycle in action.
  • Hydrologic or Water Cycle: Diagram of the water cycle and article that discusses evaporation, condensation, interception, and infiltration.
  • Hydrosphere-Atmosphere Interactions: Information about the phases of the water cycle and places where Earth's water is stored.
  • Water Cycle Basics: Details on the various steps involved in the water cycle and its importance to life on Earth.
  • Round and Round It Goes - Water Cycle: Students can click on the different parts of the water cycle to learn more or try various water cycle activities.


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