Filtration

Water filters have a long history as a method of water purification, beginning as early as 2000 b.c.e. in ancient Egypt. Filtration has evolved from the simple Hippocratic sleeve of ancient Greece, made from cloth, to the complicated solid block carbon and multimedia water filters currently on the market. Water filtration is now the premier method of water purification, removing more water contaminants, more efficiently, than any other technique.

The filtration process involves some type of filter media, over which water flows. This filter media blocks passage of contaminants through physical obstruction, chemical adsorption, or a combination of both processes. Material construction of the filter media varies widely, but the most effective medias are made from carbon or a combination of carbon with other elements. Modern filtration technology allows water filters to remove more and more contaminants through the chemical process of adsorption. In the adsorption process, contaminants are encouraged to break their bond with water molecules and chemically adhere to the filter media. Generally, water goes through several stages of filtration to ensure that each filter media will remove the ultimate number of contaminants. Water normally passes through a water filter at a relatively low speed, in order to ensure adequate contact time with the filter media. Once the water has passed through the required stages of filtration, it emerges as pure drinking water, free from contamination.

Current

Currents are large-scale water movements that occur everywhere in the ocean. The surface currents are driven by winds, while deep subsurface currents are driven by density differences in the ocean water. Ocean currents transport heat from the equator toward the poles, thereby partially equalizing surface temperatures over the earth. Ocean currents, winds, and weather patterns are closely linked. Currents can affect the food chain by transporting nutrients and plankton from one area to another. Fish congregate in high plankton areas to feed, attracting larger predators such as tuna, birds and marine mammals (and humans!). Wind Driven Currents The ocean and atmosphere of the earth are heated unevenly by the sun. More heating takes place at the equator than at the poles. This difference in temperature at the equator and the poles causes warm air to rise along the equator, and cold air to sink at the poles. Rising and sinking air creates wind, as adjacent air masses move in response..

At the North and South Poles, ocean water is cooled by the polar ice caps

and by the lack of sun. Very cold, dense water sinks and flows along the

bottom of the ocean toward the equator. Antarctic bottom currents flow past

the equator into the northern hemisphere. These polar bottom currents are

very slow moving. It may take 600 years for Antarctic bottom water to reach

into the northern hemisphere. This very cold water is full of oxygen and is the

primary source of oxygen in the deep sea.

At the equator, waters warmed by the tropical sun rise, expand, and flow

out away from the equator. Remember that the atmosphere is moving in much

the same pattern, also due to unequal heating by the sun. The world's oceans travel in well-defined circular patterns called currents which flow like rivers. When the atmosphere pushes over the surface of the ocean some of the energy goes to forming waves while the rest goes to pushing the water in the direction of the wind. North of the equator currents bend to the right; south of the equator, they bend to the left. This is called the Coriolis effect. Winds, continents and the Coriolis effect make currents flow around the oceans in huge loops called gyres.
Energy from the sun also causes currents to flow. Water near the equator is heated more than water at middle latitudes causing a surface flow toward the poles. Where two currents meet, the colder water sinks pushing warmer water up to the surface.
Read more at :

http://earth.usc.edu/~stott/Catalina/Oceans.html

Useful Water

Water is one of the commonest of all substances, and without it life would be impossible. We can live for quite some time without food, but without water we will surely die. contain of water Approximately, 70% of the earth's surface is covered with water. More than half of the human body consists of water. Water also forms a large part of the food we eat, especially vegetables and fruits. 

 In drier parts of the world where there is little rainfall, water is channeled from rivers or lakes and used to grow fruit and vegetables which provide food for mankind. In many parts of these arid regions, cultivation is not possible at all because there is no water. 

Read more at :

http://www.waterwise.org.uk/pages/fun-facts.html.

http://www.allaboutwater.org/water-facts.html.