Water is essential for the sustenance and growth of human beings as well as of all animals and plants. Three- fourths of the weight of our bodies consists of water and a part of which we get from food we eat and also from drink­ing water, tea and other liquids.

But much of the ill health in our country is largely due to lack of safe drinking water. The provision of safe and adequate water supply ranks in importance above every other public service that can be given to a community.

As water is required for many purposes, it should be ‘safe and wholesome’. It is a basic health need. It is required for domestic, public, industrial and agricultural purposes. The food and raw materials needed for the different developmental work cannot be raised without water. Water is therefore, an essential factor in the economic, social and cultural development of the country.

The Composition of Water:

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Water is composed of two gases, namely Hydrogen and Oxygen. They combine chemically to form water. For this reason water is known as a Chemical compound Water can be split up in to Hydrogen and Oxygen by the use of electricity, and on the other hand, the two gases may be made to combine to form water. Water may exist in the form of gas, liquid or solid and thus steam, mist, clouds, rain, snow and ice are all different forms of water.

Sources of Water Supply:

Before planning a scheme for ensuring safe water supply a consideration of all existing and possible sources0‘ water supply is necessary there are two main sources of water: Surface water and Ground water, Surface water originates mostly from rain water. The vast majority of Indian cities and towns depend upon surface water sources, which are (i) Impounding Reservoirs (ii) Rivers and Streams and (iii) Tanks, Ponds and Lakes.

Rain:

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Rain is the prime source of all water. It is the purest water in nature. Physically, it is clear, bright and sparkling. Chemically, it is a very soft water. But it is very difficult to store the rain water and use it for general pur­poses. Rain water tends to become impure as it passes through the atmosphere. It picks up suspended impurities from the atmosphere such as dust, soot and micro organisms there are very few places in the world like Gibraltar which depend upon rain as a source of water supply.

Reservoirs:

These are artificial lakes constructed usually of earthwork in which large quantities of surface water are stored Dams built across rivers and mountain streams also provide large reserves of surface water. The area draining into the reservoir is called ‘Catchment area’. Most of the big cities derive their water supply from impounding reservoirs; one disadvantage of storing water for a long period in reservoirs is the growth of algae and other microscopic organisms. But the reservoirs usually furnish a fairly good quality of water. The water is usually clear palatable and ranks next to rain water in purity. The water is usually soft an 1 considered to be tree of patho­genic organisms

Rivers:

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Many rivers furnish a dependable supply of water. Cities such as Delhi, Calcutta and Allahabad obtain their entire water supply from rivers. The chief drawback river water is that it is always grossly polluted and is quite unfit for drinking without treatment. So before use, the water is purified by passing it through filtering beds Hade of stone, bricks or other materials of different sizes

After being thus purified it is conveyed in large under­ground pipes and distributed throughout the city by means of smaller branch pipes made of galvanized iron or lead. These pipes are so carefully placed that foul gases, liquids and other impure matters may not be able to find their way in to the water supply through cracks and other defects.

Tanks:

Tanks are excavations in which surface water is stored. They are present almost in all states of India and are an important source of water supply. Though the water of the tanks is often used for d. inking as well as domestic purposes yet it should never be considered safe for human consumption because it is subject to unlimited possibilities of contamination, A certain amount of natu­ral purification does take place in tank water because of storage oxidation and other agencies but these are not sufficient to render the water safe.

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The sanitary quality of tank water may be considerably improved by observing the following:

(i) The edges of the tank should be elevated in order to prevent the entry of surface washings:

(ii) There should be a fence around the tank to prevent access to animals;

(iii) No one should be permitted to get in to the tank directly;

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(iv) There should be an elevated platform from where people can draw water;

(v) The weeds should be periodically removed;

(vi) The tank should be cleaned at the end of the dry season.

Inspire of these precautions, tanks are unsuitable as sources of drinking water owing to the unlimited possibili­ties of contamination. If they are to be used, the water should be disinfected and supplied through pipes,

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Ground Water:

Ground water is the cheapest and most practical means of providing water to small communities’ Ground water is superior to surface water, because the ground itself provides an effective filtering medium. The usual ground water sources are wells and springs. Wells have been classified into shallow and deep wells, dug wells and tube wells.

(i) Deep Wells:

The term ‘shallow’ has nothing to do with the depth of the well; a shallow well is one which taps the water from above the first impervious layer in the ground. But a deep well is one which penetrates the first impervious .layer in the ground and taps the water lying beneath the impervious layer.

(ii) Artesian Wells:

This is a kind of well in which the water rises above the level of ground water, because it is held under pressure between two impervious strata. Artesian wells are not common in India.

(iii) Dug Wells: Wells may also be classified accord­ing to the method of construction, in to Dug wells and Tube wells. Dug wells are by far the commonest type in India. Two types of dug wells exist in our rural areas: (a) The unlined cachucha well and (b) The masonry or puce well. Cachucha well is a hole dug in to the water bearing stratum. -The puce well is an open well built of bricks or stones. In these wells, there is considerable personal contact between the user and the water. Some people may even wash their faces, hands and feet which is a common Indian custom. The open dug wells are a health hazard to the community.

(iv) Tube Wells:

A tube well consists of a pipe sunk in to the water bearing stratum and equipped with a screen at the bottom and hand pump at the top. Water obtained from this source is the best and safest for drinking purpose. Deep tube wells or bored wells are sunk by drilling through successive substrata of gravel or rock until a suitable supply

Of ground water is located. They may be several hundred feet deep and require complicated mechanical drilling equipment and skilled engineering direction. Though these types of wells are costly to construct and to operate yet the water is pure and safe for drinking.