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The Water Cycle and Water Sources

The water cycle describes the continuous movement of water, moving through the Earth connecting oceans, land and the atmosphere, in different physical phases from liquid to vapor to ice and back again.  This continuous cycle of the movement of water has been happening for billions of years and all life on Earth is depending on this cycle. 

Water evaporates from the Earth's surface, rises up into the atmosphere, cools down condensing into rain or snow in clouds, then falls back to the surface as precipitation. This falling water collects in rives and lakes, or becomes captured in porous rock layers, with a large amount of this water eventually flowing back into the oceans, where it will start the evaporation process over again. 

Check out these
videos on
the water cycle:


CC Kids
"The Great Water Adventure"




 
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Water Sources 

Our drinking water comes from either surface, ground or rain water.

Surface water refers to any flowing bodies of water, including lakes, rivers, streams, reservoirs, or ocean and is generally refilled via precipitation. Surface water is more easily accessible than groundwater, but is not usually a good source of drinking water, due to the high levels of contaminants which get into the open water source. Therefore, surface water usually should be treated and filtered before it is safe to drink. However, surface water bodies are very important renewable resources and are huge storehouses of freshwater. 

Groundwater, on the other hand, is a part of the natural water cycle, where water continuously moves within the Earth and the atmosphere. Liquid water flows across land, enters the ground, taken up by plants, then evaporated from plants into the atmosphere, starting the cycle again with precipitation. Groundwater is water stored in spaces deep underground in between rock particles, mostly within 0.8 km or less from Earth’s surface. We access this water by drilling or digging wells. Groundwater is generally of good quality without microbes in it, if kept far from a polluting source.

Rainwater can also be a good source of water for families and communities living in areas where it rains a lot. The quality of rainwater is usually very good, but has to be collected from a clean surface (such as a roof), then stored well in a protected and covered cistern. 

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Surface Water: lakes, rivers, streams, oceans...

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A Rainwater Harvesting System.

Source: Center for Affordable Water and Sanitation Technology (CAWST), Introduction to Household Rainwater Harvesting, November 2011 Manual, licensed under CC BY-SA 4.0

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Water Cycle and Sources
CAWST: Water Hygiene and Sanitation Presentation, February 2011

Click here for an interactive poster of the Water Cycle

Credit: U.S. Geological Survey

Videos credit: Crash Course Kids, You Tube