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Did you know?
Over the past decade, the Yellow River in China has not reached the Bo Hai Sea on average for three to four months every year. Throughout the 1990s its waters, once a torrent to be revered and feared, have trickled out as far as 600 km inland. The flow of Amu Darya and Syr Darya Rivers in Central Asia that once fed the Aral Sea which borders Kazakhstan and Uzbekistan in Central Asia have been reduced by three-quarters since the late 1960s. As a consequence, the sea has receded by up to 100 km. Two-thirds of its volume has been lost. We are all aware that more than 2/3 of the earth’s surface is made up of water, in fact when the first astronauts viewed the earth from the moon it looked all blue, this is because the percentage of water is so high. Fresh water represents less than ½ of 1% of the total water on the earth’s surface. The rest is either seawater or locked up in icecaps or soil. Worldwide the consumption of water is doubling every 20 years –more than twice the rate of increase in population.
The major sources of water pollution in India is domestic sewage, the bulk of which is released untreated; industrial waste; and agriculture runoff. Only one-tenth of waste-water generated in cities of India is treated. The River Yamuna is a source of drinking water for two big cities – Delhi and Agra. All the waste water from these cities flow back into the river while industries dump all their chemical waste into it. Over exploitation of groundwater in certain states has resulted in long term decline in water levels with associated adverse cosequences such as land subsidence and deterioration of ground water quality.
A large amount of water is being wasted in agriculture, industry and urban areas. It has been estimated that with available technologies and better operational practices, agricultural water demand could be cut by about 50%, and in urban areas by about 1/3rd without affecting the quality or economics of life. But most governments do not have adequate laws or regulations to protect their water systems. Among the most dangerous of all water pollutants is fuel oil. Oil spills from tankers at sea or leaks from underground storage tanks on land are very difficult to control as oil tends to spread very fast, affecting a large area in a very short time. Oil spills at sea decrease the oxygen level in the water and cause grave harm to the creatures living in the sea. The per capita availability, in terms of annual average utilizable water resource of India, which was 3450m3 in the year 1951, is now 1250m3 and would reduce to 760m3 . in the year 2050 placing it in the category of water stressed.
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Only
10 % of the water from River Nile in Egypt reaches the Mediterranean
Sea. This small amount is heavily polluted with agricultural, industrial,
and municipal wastes. 
Even as early as 3000-2500BC, during
the period of the Indus Valley Civilization people were aware of the
benefits of a good drainage system. From excavations in the Indus
Valley and other sites in India belonging to the period it has been
proved that they had a very well laid out drainage system, with water
from houses flowing into the drains along the roads, these drains
in turn led to the rivers.
Dams are mainly built across rivers for either generating
hydroelectricity or for providing water for irrigation or domestic
purposes. The construction of large dams leads to resettlement and
rehabilitation of a large number of people living on the submerged
side of the dam. Mini and micro hydel projects do not cause any damage
to the environment and are therefore cleaner in all ways. Large dams
in the USA are being dismantled to restore riverine ecosystems and
return the nation’s rivers to ‘good health’. This move
is expected to inspire the removal of other dams whose environmental
cost outweighs their benefits.