Environmental Engg. 3(2+1)

Lesson-1 Water supply system

HISTORICAL DEVELOPMENT

Since old ages, there has been search for pure water.  The story of water supply begins with the growth of ancient capitals, religious towns, etc.  Some of the earliest civilizations flourished along the banks of the rivers Tigris, The Euphrates, the Nile and the Indus. Archaeological excavation reveals that as early as 2500 BC, the people of Harappa, Mohanjodaro and around Indus river basin had well organized water supply systems.  Rig Veda makes a mention of digging of wells.  Similarly, Indian epics like Ramayana and Mahabharatha make mention of wells as the principal source of water supply.  Those wells are mostly of shallow depth, dug near river banks.  As the need for water increased and tools were developed, wells were made deeper. Brick-lined wells were built by city dwellers in the Indus River basin as early as 2500 B.C., and wells almost 500 metres (more than 1,600 feet) deep are known to have been used in ancient China. 

Apart from India, other major civilizations of the World used wells for their settlements which were located slightly away from springs, lakes and rivers.  However, these wells caused water supply problems in times of drought.  Hence, Cisterns were constructed for collecting rain water while reservoirs were constructed to store water from streams and rivers during monsoon period.  The stored water was conveyed to towns through masonry conduits and aqueducts. 

The need to channel water supplies from distant sources was an outcome of the growth of urban communities. Among the most notable of ancient water-conveyance systems are the aqueducts built in the Roman Empire. Some of these impressive works are still in existence.

There was not much drastic improvement in water supply systems in the middle ages.  The development in the field of water supply system remained almost static until 17^th and 18^th centuries but it was again confined to the Europe. It was only the 19^th century that the Americans had developed more advanced systems for water supply, its treatment and disposal. The scientific discoveries and engineering inventions of the 18^th and 19^th centuries created centralized industries to which people flocked for employment.  This caused serious water supply problems in those cities and towns.  No great schemes of water supply were started until the Industrial Revolution had well passed its first half century.  The development of large impounding reservoir was largely due to the necessity of feeding canals constructed during the first phase of the Industrial Revolution.

Water treatment is the alteration of a water source in order to achieve a quality that meets specified goals. At the end of the 19^th century and the beginning of the 20^th, the main goal was elimination of deadly waterborne diseases. The treatment of public drinking water to remove pathogenic, or disease-causing, microorganisms began about that time. Treatment methods included sand filtration as well as the use of chlorine for disinfection.

The first known illustrated description of sand filters was published in 1685 by Luc Antonio Porzio, an Italian physician.  The first filters built in the USA were of the slow-sand type, similar to British design. About 1890 rapid-sand filters were developed in the United States, and coagulants were later introduced to increase their efficiency.

It is astonishing to note that to the middle of the nineteenth century there was no marked progress in sewerage. In 1842, sewerage system was installed in the city of Hamburg, Germany.  In 1847,  the connection between water supply and sewage pollution was proven in London, England.

The earliest recorded knowledge of water treatment is in the Sanskrit medical lore and Egyptian wall inscriptions. Sanskrit writings dating about 2000 B.C. tell how to purify foul water by boiling in copper vessels, exposure to sunlight, filtering through charcoal, and cooling in an earthen vessel.

ESSENTIALS OF ANY WATER SUPPLY PROJECT / SCHEME

The most important aspect of any water supply scheme is the choice of source of supply.   The source should be permanent, reliable and should provide water with minimum impurities.   Lakes, streams, springs, are surface sources, whereas wells, infiltration galleries are ground sources.  The existence of such a kind of water supply scheme will help in attracting industries and thus promote industrialization and ensuring better living standards.

After the selection of source of water, the next step is to construct suitable intake works to collect and carry water to treatment plants for treatment.  The treatment of water depends on the source of supply, and the amount and nature of impurities present in it.  Water generally has suspended, dissolved, and colloidal impurities.   Underground sources are comparatively clear, cool and free from bacteria.  However, the treatment may be necessary to remove hardness, iron and manganese.  Surface waters may require chemical treatment with coagulation, flocculation and sedimentation, prior to filtration through sand filters.

Aeration and activated carbon process etc. are used for the removal of tastes and odours.  Chlorination is almost always essential for disinfection.  To prevent cavity formation in teeth, sometimes, soluble fluorides are also mixed with water. 

Water is carried through pipes from source to treatment plant, and then from treatment plant to distribution system.  Distribution system consists of large arterial mains, distribution mains, minor distributors and appurtenances, including valves, meters and hydrants.  Treated water is stored in clear water reservoirs from where it is distributed to the consumers through distribution system of pipes.  In low level areas water will flow directly under gravity but for high level areas, elevated tanks and pumps will have to be installed.  The complete outline of water supply system (Fig. 1) is explained in the following flow chart.

 Fig. 1 Outline of water supply system

Preliminary investigations for water supply scheme

Any water supply system / project has to be meticulously planned and studied for various view points.  The following points should be looked into while considering any water supply system

Sources of water supply

It is quite clear that the success of a water supply scheme entirely depends on good sources of water supply.  The sources should be selected while keeping in view its adequacy throughout the year, quality of water and cheapness.  The present source of water supply should also be adjusted properly in the new water supply scheme.   

Population

From the available census of previous years, the present population should be determined and it is a general practice to make the scheme to accommodate population after three or four decades.

Financial aspects

The availability of fund for the completion of the water supply scheme should be obtained in the initial stages of the scheme itself.  The scheme should then be adjusted according to the fund available.  Every step should be taken to make the scheme as economical as possible and to take the maximum advantage of it.

Quantity of water

The demand of water depends on various uses such as domestic, industrial, public, trade, etc.  The rate of consumption per capita should be decided by carefully considering all these possible uses.  This rate, when multiplied by the population, gives the total quantity of water required for the water supply scheme. 

Quality of water

The quality of available water decides the line of treatment of water.  The more pure water is, the less it the cost of the treatment. Hence, samples of available sources of water should be taken and properly analysed and the results of various tests should be thoroughly studied to suggest an economical water supply scheme for the localit

Sanitary survey

The sanitary survey of area surrounding the available water sources should be carefully carried out.  Such a survey helps in estimating the possible pollution or contamination of water from such sources.  The sanitary survey includes the collection of information regarding the likely sources of water pollution

Topography

The topographical map of the area to be served by the scheme should be prepared and it should be studied in relation to low lying area, ridges, density of population, etc.  The study is essential to evolve a simple but cheap water supply scheme.

Town development trend

The trends of town development in future should be predicted and properly adjusted in the water supply scheme.  Such trends may take various forms such as possibility of new industries, public recreation centres, public institutions, residential blocks, etc.