The Water Cycle (also known as the hydrologic cycle) is the journey water takes as it circulates from the land to the sky and back again.
The Sun's heat provides energy to evaporate water from the Earth's surface (oceans, lakes, etc.). Plants also lose water to the air (this is called transpiration). The water vapor eventually condenses, forming tiny droplets in clouds. When the clouds meet cool air over land, precipitation (rain, sleet, or snow) is triggered, and water returns to the land (or sea). Some of the precipitation soaks into the ground. Some of the underground water is trapped between rock or clay layers; this is called groundwater. But most of the water flows downhill as runoff (above ground or underground), eventually returning to the seas as slightly salty water.
The Sun's heat provides energy to evaporate water from the Earth's surface (oceans, lakes, etc.). Plants also lose water to the air (this is called transpiration). The water vapor eventually condenses, forming tiny droplets in clouds. When the clouds meet cool air over land, precipitation (rain, sleet, or snow) is triggered, and water returns to the land (or sea). Some of the precipitation soaks into the ground. Some of the underground water is trapped between rock or clay layers; this is called groundwater. But most of the water flows downhill as runoff (above ground or underground), eventually returning to the seas as slightly salty water.
To sum up:
There are six important processes that make up the water cycle.
1. Condensation - the opposite of evaporation. Condensation occurs when a gas is changed into a liquid.
2. Infiltration - Infiltration is an important process where rain water soaks into the ground, through the soil and underlying rock layers.
3. Runoff - Much of the water that returns to Earth as precipitation runs off the surface of the land, and flows down hill into streams, rivers, ponds and lakes.
4. Evaporation - the process where a liquid, in this case water, changes from its liquid state to a gaseous state.
5. Precipitation - When the temperature and atmospheric pressure are right, the small droplets of water in clouds form larger droplets and precipitation occurs. The raindrops fall to Earth.
6. Transpiration - As plants absorb water from the soil, the water moves from the roots through the stems to the leaves. Once the water reaches the leaves, some of it evaporates from the leaves, adding to the amount of water vapor in the air. This process of evaporation through plant leaves is called transpiration.
More information in: http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Watercycle.shtml
Do the gap filling in: http://education.jlab.org/reading/water_cycle.html
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