Source of Water

For centuries man has used the water available to him in rivers, lakes and streams. It has provided both food and drink and been used for recreation, transport, energy, cooling and waste disposal. To learn a few more interesting facts about water refer to Highlight 1. 

Let us now try to address ourselves to some basic questions related to water, to utilisation and quality : 

What are the various natural sources of water? 

The oceans, seas, rivers, lakes, springs, water falls, glaciers or the snow capped mountains, rain, the ponds, the groundwater etc. Of these, water in rivers, lakes, springs, ponds, ground water are referred to as fresh water and form the main sources of water in nature. 

Fresh water from inland sources can be broadly classified  into, i) Surface Water comprising rivers, lakes and ponds and ii) Ground Water comprising of wells and springs. A portion of the water falling on land soaks into the ground. This is stored in underground  tunnels as groundwater. Groundwater is pure as it has already percolated  through the soil and purified by a natural process of filtration. This is increasingly being preferred for use by people. But finding adequate groundwater sources for supplying large urban populations is difficult. Cities that do have good groundwater supplies benefit, because the cost of treatment is minimal. The treatment basically removing excessive minerals. Often the water is pure enough so that chlorine or other chemicals are not needed to make it usable, even for drinking. 

How many of these are sources of potable water? 

Of all the water available on earth, potable or water fit for human consumption can be found only in the rain water, inland surface water bodies like rivers, lakes, ponds and underground water from wells and handpumps. The major portion in the oceans and seas is salty and cannot be consumed as such. 

What is the hydrological or water cycle? 

All the water on planet Earth is constantly on the move constituting what is called the hydro logical cycle. The hydrological cycle starts with evaporation. Every tear, sea water and surface water from the land is evaporated by the sun's warmth. When this eventually falls again as rain or snow, it falls on the land and sea in different proportions. The portion which falls on the land eventually runs back into the sea but, in the meantime, those who live on land where it falls have the benefit of it. Some of the water falling on the land runs off in streams, or it may be held in lakes or ponds. From these bodies or stationary reservoirs, water is evaporated, going back into the sky to form moisture-laden clouds that eventually lose  their water again as rain or snow. 

Most of the Earth's water, however, participates in the vast and endless hydrological cycle that provides all the world's fresh water, and acts as a giant purification system. This is because nearly all pollutants evaporate at much higher temperatures than water. So when the evaporated water condenses and returns as rain or snow, it is pure. 

Some of the water falling on land soaks into the ground. This groundwater also eventually returns to the atmosphere but the cycle is much slower. It is drawn into the plants by their roots and then moves up the stems and leaves. Large amounts escape through the leaves by a process called transpiration. Green plants over the earth's land surface thus move water steadily back into the atmosphere. We mentioned earlier that plants use water to manufacture food. In fact, using water and carbon dioxide, plants make starch.

Why do our ground water suppliers need to be protected? 

The water -table  lies at the upper level of the zone of ground water below the Earth's surface. Where there are lakes and rivers, the water-table is near the surface. But although ground water is usually clean and pure, it is by no means sealed off from human activity and nor is it necessarily static. Ground and surface water are linked together by a series of continual interactions - interactions that serve to keep underground supplies topped up b;t  may also be a source of pollution. 

The rate at which ground water is renewed depends upon many factors - but the nearer it is near the surface, the faster it is renewed. Near the water-table itself, renewal may take as little as a year; in deep underground aquifers, renewal may take thousands of years. If these deep water stores-which  are virtually underground lakes of fossil water ever become polluted, their contamination is near permanent and irreversible. 

When ground water is over- exploited by too many wells, the water- table may be lowered as a result. Even if there is sufficient water to recharge the aquifer, it may be only partly replenished if it is made of clay or soil with variable porosity. In this case, once it dries out, it will shrink and be unable to hold as much water as it did previously. 

In this situation, precious water is not the only thing to be lost. If underground clay and other materials shrink sufficiently, there is likely to be land subsidence (sinking of land) at the surface. This can have serious consequences. Better planning and improved understanding of the links between surface and ground water are needed to avoid such catastrophes. 

What is the salinity factor? 

The problem of excessive salinity is caused by inefficient irrigation. What happens is that the rain that filters down through the layers of damp soil, sand and clay to recharge underground aquifers, dissolves and collects different salts on its way. Most groundwater therefore contains some salts. These salts may be brought to the surface through the irrigation of badly drained land. The water-table rises and eventually the land becomes waterlogged. Salts from the ground water can then rise to the surface, where evaporation concentrates them. In the end saline or alkaline soils will be formed on which little will grow and yields will continue to drop until the land is either abandoned or effectively drained. 

Why is water becoming scarce? 

Until very recent times, most people took water for granted as  free, or nearly so, and certainly inexhaustible. But along with the rapidly increasing population have come severe water shortages. In days gone by, people built their homes near a good source of water,  and if that supply dwindled or went dry, they moved. Now there are really no more places where people can move to find good, clean water so easily. And because people are spread widely over the world, water must be transported long distances to supply their needs. 

As we are developing we are making increasing demands on water resources. Water requirements for agriculture, mining, power generation and water supply to pressure on declining water supplies, Further quality of water is also deteriorating because of increased levels of pollution and increases in salinity. 

What are the various types of wells? 

Wells are man-made artificially dug holes or pits in the earth to tap the ground water. There are various types of wells. Let us talk about these types in some detail. 

Shallow Wells : A shallow well is one in which the water is obtained above the first impervious layer in the ground. Most of the wells in our country are of this take suitable precautions in keeping such wells safe. Otherwise they can pose a major health hazard for the local community. 

Deep Wells: A Deep Well is one in which the water is obtained from below the first impervious layer. Though comparatively safer, the deep wells can also be contaminated if left open or if  they are poorly constructed and unprotected. Besides this general classification wells can also be classified into various kinds depending on regional variations e.g. 'Step Wells'  or 'baodis'  'pecular'  to Rajasthan, 'Draw Wells' or 'Kuan',  'Dug Wells' etc. In addition to various health hazards posed by wells, step wells may provide the additional risk of Guinea-worm infection. 

Tube Wells : With the demand for land and water shooting up, a newer version of the well called the tube well is becoming increasingly popular. It has the added advantage of being both safe and cheap when compared to other sources. The only drawback is that there is an element of maintenance of the hand pump. Like all machinery, this needs frequent servicing. The average life of a tube well is about 10 years. If maintained properly it can serve upto 30 years.