We all know that three-fourth of the earth's surface is covered by water. If there is more water than land on this earth, why do so many countries face water scarcity? Let us understand the distribution of water bodies on earth.

Is all the water on earth available to us? The following table gives the distribution of water bodies in percentage:

• Oceans: 97.3
• Ice-caps: 02.0
• Groundwater: 0.68
• Fresh Water Freshwater lakes: 0.009
• Inland seas & Salt lakes: 0.009
• Atmosphere : 0.0019
• Rivers: 0.0001

Water is absolutely essential for survival. Water alone can quench our thirst when we are thirsty. Now, don�t you think we are wasting a precious resource when we use water carelessly?

OCEAN CIRCULATION

Unlike the calm waters of ponds and lakes, ocean water keeps moving continuously. It is never still. The movements that occur in oceans can be broadly categorized as waves, tides, and current

Waves: When the water on the surface of the ocean rises and falls alternately, they are called waves. During a storm, the winds blowing at a very high speed form huge waves. These may cause tremendous destruction. An earthquake, a volcanic eruption, or underwater landslides can shift large amounts of ocean water.

As a result, a huge tidal wave called a tsunami, which may be as high as 15m., is formed. The largest tsunami ever measured was 150m. high. These waves travel at a speed of more than 700 km. per hour

Tides: The rhythmic rise and fall of ocean water twice in a day is called a tide. It is high tide when water covers much of the shore by rising to its highest level. It is low tide when waterfalls to its lowest level and recedes from the shore.

The strong gravitational pull exerted by the sun and the moon on the earth�s surface cause the tides. The water of the earth closer to the moon gets pulled under the influence of the moon�s gravitational force and causes high tide. During the full moon and new moon days, the sun, the moon, and the earth are in the same line and the tides are highest. These tides are called spring tides.

But when the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of the sun and earth resulting in low tides. These tides are called neap tides.

High tides help in navigation. They raise the water level close to the shores. This helps the ships to arrive at the harbor more easily. The high tides also help in fishing. Much more fish come closer to the shore during the high tide. This enables fishermen to get a plentiful catch. The rise and fall of water due to tides are being used to generate electricity in some places.

OCEAN CURRENTS

Ocean currents are streams of water flowing constantly on the ocean surface in definite directions. The ocean currents may be warm or cold. Generally, the warm ocean currents originate near the equator and move towards the poles. The cold currents carry water from polar or higher latitudes to tropical or lower latitudes.

The Labrador Ocean current is a cold current while the Gulf Stream is a warm current. The ocean current influences the temperature conditions of the area. Warm currents bring about warm temperatures over the land surface. The areas where the warm and cold currents meet provide the best fishing grounds in the world.

Seas around Japan and the eastern coast of North America are such examples. The areas where a warm and cold current meets also experience foggy weather making it difficult for navigation.

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