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Clean, fresh water is essential for nearly every human activity. Perhaps more than any other environmental factors, the availability of water determines the location and activities of humans beings. Almost all agricultural operations which supply food to humanity need water.
Of the total water available on earth, only 3% is fresh water.
1. Glaciers, ice and snow : Of the 3 percent of all water that is fresh, about three - fourths is tied up in glaciers, ice caps and snowfields. They occur only at high altitudes or high latitudes.
2. Ground water : After glaciers, the next largest reservoir of fresh water is held in the ground in ground water. Water held in the lower soil layers is known as water table. Porous- water bearing layers of sand, gravel and rock are called aquifers.
3. Lakes and Ponds : Lakes are inland depressions that hold standing fresh water year around. Ponds are small temporary or permanent bodies of shallow water. While lakes contain nearly one hundred times as much water as all rivers and streams combined, they are still a minor component of total world water supply.
4. Wet lands : Bogs, swamps, wet meadows and marshes play a vital and often a minor role.
At least one billion people or nearly 20 percent of the world's population, lack safe drinking water. The W.H.O. considers 53,000 gallons of good water per year to be the minimum for a healthful life. Some forty countries (including island nations, Middle East countries) in the world fall below this level.
1. Natural forces
Deficits are caused by natural forces such as poor rain fall and hot winds, rivers changing courses.
2. Human causes
Include increased population, rapid urbanization, over grazing by cattle, improper cultivation methods, poor sewage systems, inadequate finances for providing infra structures.
3. Depleting ground water
Ground water is the source of nearly 40 % water for agricultural and domestic use in most of the countries. Nearly 95% of rural population depends on groundwater for drinking and other domestic purposes. Over
use of the supplies causes several kinds of problems, including drying of wells, natural springs and disappearance of surface water features such as wetlands, rivers and lakes.
In many parts of the world, groundwater is being withdrawn from aquifers faster than natural recharge can replace it. On a local level this causes a level of depression in the water table. A heavily pumped well can lower the ground water table so that nearby shallower wells go dry. On a broader scale, heavy pumping can deplete a whole aquifer. Many aquifers have slow recharge rates, so it will take thousands of years to refill them once they were emptied.
4. Salt water intrusion
Many parts of the world are losing freshwater sources due to saltwater intrusion. Over use of under ground freshwater reservoirs often allows salt water to intrude into aquifers and affect the water table.
5. Loss of free flowing rivers
Loss of free flowing rivers that are either drowned by reservoir impoundments or turned into linear, sterile irrigation channels is yet another cause for freshwater crisis.
6. Evaporations, leakage and siltation
It happens in freshwater lakes, ponds and dams.
On a human time scale, the amount of water on the earth is fixed, for all practical purposes. There is little we can do to make more water. However, there are several ways to increase local supplies.
a) Seeding clouds
Seeding clouds with dry ice or potassium iodide particles sometimes can initiate rain if water laden clouds and conditions that favour precipitation are present.
Desalination of ocean water is a technology that have great potential for increasing fresh water. The common methods of desalination are distillation (evaporation and recondensation) or reverse osmosis (forcing water under pressure through a semipremeable membrane whose tiny pores allow water to pass but exclude most salts and minerals). Although desalination is still three to four times more expensive than most other sources of freshwater, it provides a welcome water supply in such places like Dubai, Oman and Bahrain where there is no other access to fresh water.
c) Dams, Reservoirs, Canals and Aqueducts
It is common to trap run off with dams and storage reservoirs and transfer water from areas of excess to areas of deficit using canals, tunnels and underground pipes.
d) Watershed management
A series of small dams or tributary streams can hold back water before it becomes a great flood. Ponds formed by these dams provide useful wildlife habitat and stock-watering facilities. Small dams can be built with simple equipment and local labour, eliminating the need for massive construction projects and huge dams.
e) Rain water harvesting
The activity of collecting rainwater directly or recharging it into ground to improve ground water storage in the aquifer is called rain water harvesting. By rainwater harvesting the ground water can be conserved, water table depletion can be reduced and also sea water intrusion in coastal areas can be arrested. To recharge the groundwater rainwater that falls in the terrace of the buildings and in the open space around the buildings may be harvested. Roof top rain water can be diverted to the existing open / bore well. Rainwater available in the open spaces around the building may be recharged into the ground by the following simple but effective methods.
The Government of Tamilnadu leads the nation in implementing rain water harvesting programme. It has made it mandatory for all houses and buildings in the State to install rain water harvesting facility.
f) Better agricultural practices
Sound farming and foresting practices can reduce runoff. Retaining crop residues on fields reduces flooding. Minimizing ploughing and forest cutting on steep slopes protects watersheds. Wetlands conservation preserves natural water storage capacity and aquifer recharge zones.
g) Domestic conservation
We could save as much as half of the water we now use for domestic purposes without great sacrifice or serious changes in our lifestyles. The use of washing machines, dish washers and low volume shower heads can reduce water loss.
h) Industrial conservation
Nearly half of all industrial water use is for cooling of electric power plants and other industrial facilities. By installing dry cooling systems, this could be avoided. Cooling water can be recharged, some industrial wastewater may be treated, recycled and reused.
i) Saving water -an individual's role
As an individual you can conserve water by the following methods.
� Take shorter showers.
� Don't wash car and two wheelers often
� Don't allow tap run while washing hands, dishes, food or brushing your teeth unnecessarily.
� In your lawn consider planting native plants, a rock garden or some xerophytic landscaping.
� Use water conserving appliances : low - flow showers and low -flush toilets.
� Use recycled water for lawns, house plants and car washing
� Check taps for leaks
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