The choice of source of water supply to a town or city depends on the following factors: 1. Location 2. Quantity of Water 3. Quality of Water 4. Cost.
Factor # 1. Location:
The source of water should be as near to the town as possible. If there are both surface and ground sources available to the town the selection will be decided by considering other factors also. If there is no river, stream or reservoirs, the city will have to depend on the underground source of water when there is no other alternative.
It has been found that mostly big-cities develop near rivers to avoid difficulties in tapping water from underground sources. But if ground water is available in abundance some important cities like Chandigarh, also develop near them.
Factor # 2. Quantity of Water:
The source of water should have sufficient quantity of water to meet up all the demands of city such as domestic, industrial, fire-fighting, public etc. throughout the year. There should be sufficient extra quantity of water to be required in future while expansion of city is done. Source of water should be able to meet the maximum demand in dry weather also.
Factor # 3. Quality of Water:
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The quality of water should be good which can be easily and cheaply treated. It should not contain disease germs or other pathogenic bacteria which may endanger the health of the public. Therefore as far as possible the water of the source should be wholesome, safe and free from pollution.
Factor # 4. Cost:
The cost of water supply project should also be taken into account while selecting the source of water. The cost of water supply scheme depends on many factors as system of supply, ground levels of city, distance between source and distribution ground levels of city, distance between source and distribution system etc.
If the water flows under the gravitational force it will be cheap, but if it is to be pumped it will be costly. Similarly the cost will directly depend on the distance between the source of water and city, if the distance is more it will be costly.
The selection of the source of water-supply is done on the above points and the source which will give good quality and the quantity at low cost will be selected. This economical policy may lead the adoption of both surface and ground water source of the supply of water to very big cities.