Source Selection Criteria
Souces of water may be defined as the place from where water is obtained. Water is primarily obtained from precipitation and majority of precipitation is rainfall. At beginning, rain water is pure. On the way of falling to the ground through atmosphere, it is mixed with dust, gases etc.
A. Surface Sources: Surface sources is the place on the surface of earth where water can be obtained easily for consumption . Quantity of water in the surface sources may be sufficient and quality may be acceptable. Sometimes treatment may be required for consumption. The various surface sources can be classified as
- Stream
- River
- Pond
- Lake
- Sea
- Stored rain water
- Waste water reclamation
- Fog water harvesting
- Impounded reservoir
B. Ground Sources: Ground sources are that place from where we can derive water contained in the water bearing strata or aquifer below the ground surface. The water quality of ground sources depends upon the characteristics of percolating water which may contain herbicides, pesticides and nutrients from agricultural land as well as minearls, salts and other impurities from soil layers during infilteration process. The water quality of ground water is generally good than surface water due to natural filteration capability. The various ground sources can be classified as
- Spring
- Infiltration Galleries
- Infiltration wells
- Porous pipe gallery
- Artesian well
- Well
- Open or dug or draw well
- Tube wells : Strainer type, Cavity type, Slotted type and perforated pipe
Among the Surface and ground sources, If spring source is adequate for the area and water quality is good, priority is given to spring. Otherwise we look for other source like as stream or river then after infilteration gallery and infilteration well. If the river or stream in the area, the ultimate source may be tube well (again ground source).
Before selection of the sources of water, we should consider for the several factors.
1. Location: It should be near to consumer's area or town as far as possible so that cost of transmission can be reduced. If source is located at higher elevation, water can be supplied by gravity flow and saves pumping cost.
2. Quantity of water: Source should have sufficient quantity of water to meet the demand for the design period in the wet and dry seasons also. Two or more sources can be joined for required quantity. If possible, there should be sufficient quantity for future extension of Project.
3. Quality of water: The water in the source sould be safe, free from pathogenic bacteria, germs, pollution and so that water can be cheaply treated to supply wholesome water.
4. Cost: Souce should be able to supply water of good quality and quantity at the lesser cost. The cost depends upon location, ground level of city and source, distance between source and distribution area etc. Gravity system of flow is generally cheaper. Lesser the impurities, lesser will be the treatment and cost is reduced. Lesser the distance between the area of distribution and source requires lesser length of pipe and lesser number of appurtenances and cost is reduced. Cost analysis is necessary for various options and suitable one is selected for water supply purpose.
5. Sustainable and Safe: Source should be long lasting for the design year and safe from flood, landslides, cattle and pedestrians etc.
6. Reliable: It should be consistent in discharging to meet the design year demand.
7. Non conflict among water users: It is the major point which should be compulsorily considered to select the source. If there is conflict among water users, the source can be selected only after its settlement.
