SOURCES OF WATER
The main sources of water on the Earth are rainwater water, surface water and underground water.
Rainwater
The main source of natural water on the Earth is rain. This is the purest form of water. But, while falling down to the Earth, rainwater gets polluted with dust particles and some dissolved gases.
Surface Water
Surface water is the water that collects on the surface of the Earth. This includes water present in oceans, seas, lakes, rivers and wetlands. Seas and oceans cover almost 70% of the Earth's surface. Water in the rivers comes mainly from rain and melting of snow from the Hills and Mountains. Rivers flow down from the hills and over the plains and finally drain into seas and oceans. They carry a lot of minerals and suspended impurities. Hence, river water is unfit for direct consumption. water in the sea and oceans has dissolved salts, especially common salt and hence is salty or saline. This condition of seawater is called salinity. The efforts being made to remove salt from sea water and make it fit for drinking and other purposes is known as desalination. This method is very expensive and involves high costs.
Groundwater
Groundwater or underground water is present below the Earth's surface. Rainwater penetrates through the ground and is stored over the non-porous layer of rocky bed. The study of groundwater is known as hydrogeology.
The process of seeping of water under the ground is called infiltration. This reservoir formed above the impervious layers of rock or clay is termed as aquifer.
The area where water fills the aquifer is called the saturated zone. The upper layer of this zone is called the water table. Water table may be deep or sallow and may rise or fall depending on many factors.
Heavy rains or melting snow may cause the water table to rise while heavy pumping of groundwater supplies may cause the water table to fall. Underground water comes to the surface through spring and wells. In wells, a boring is done, till the water table is reached. This water is pumped to the surface using a hand pump, tube-well or electric pump.
Sometimes the water level in the water table on two sides is higher than the middle. As water seeks its own level, the water rises and forces itself out of the earth's surface. This forms a well called the artesian well. Springs form when groundwater finds an outlet in porous rock.
Spring water and well water are usually clear and free of suspended materials as they have percolated through several layers of sand, gravel and clay and hence are naturally filtered.
Groundwater supplies are replenished or recharged by rain that seeps down into the cracks beneath the land's surface.
In some areas of the world, people face serious water shortage because groundwater is used faster than it is naturally replenished. In some areas, groundwater is polluted by human activities.
Sometimes the water level in the water table on two sides is higher than the middle. As water seeks its own level, the water rises and forces itself out of the earth's surface. This forms a well called the artesian well. Springs form when groundwater finds an outlet in porous rock.
Spring water and well water are usually clear and free of suspended materials as they have percolated through several layers of sand, gravel and clay and hence are naturally filtered.
Groundwater supplies are replenished or recharged by rain that seeps down into the cracks beneath the land's surface.
In some areas of the world, people face serious water shortage because groundwater is used faster than it is naturally replenished. In some areas, groundwater is polluted by human activities.
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