As we know every water is not suitable for human beings in the same way every water is not suitable for plant life. Water which contains impurities is injurious to plant growth and is not satisfactory for irrigation. Selection of a source of water for irrigation depends upon the following factors:
a) Quantity needs
b) Quality factors
d) Conflict and competition for water
Water source selection for irrigation
a) Quantity needs:
The source selected for irrigation should have adequate quantity of water to fulfil the water requirements of the command area. If water is not available in adequate quantity, there will not be desirable yield of the crops in one hand and conflict between farmers in another hand.
b) Quality factors:
The concentration and composition of dissolved constituents in water determines the quality. The various impurities which make the water unfit for irrigation are as follows:
i) Sediment concentration in water
ii) The total concentration of soluble salts
iii) Potentially toxic elements
iv) Bacterial contamination
i) Sediment concentration in water:
The result of sediment gift within the irrigation water depends upon the sort of irrigated land. When the sediment from water is deposited on sandy soil the fertility is improved but if the sediment has been derived from the eroded areas it may reduce the fertility or decrease the soil permeability. Sedimented water creates troubles in irrigation canals by causing canal siltation and by increasing maintenance costs.
ii) The total concentration of soluble salts:
Salts of calcium, magnesium, sodium and potassium present in irrigation water may cause injurious to plants. When these salts are present in the excessive amount they reduce the osmotic activities of plants and may cause injury to plant growth.
At the beginning of irrigation with undesirable water, no harm may be evident but with the passage of time, the salt concentration in the soil will reach a harmful level.
iii) Potentially toxic elements :
A large variety of components like Selenium may be toxic to plants. Traces of Boron are essential to plant growth but its concentration above 0.3 ppm may prove toxic to certain plants. Selenium even in low concentration is toxicant and should be avoided. Boron is essential to present in various soaps. Therefore soap water should be used with great care in irrigation.
iv) Bacterial contamination:
Water contaminated with bacterias may be useful or harmful to plants according to the nature of bacteria’s towards plants.
c). Location of source:
Source of irrigation canal should be as near as possible to the command area. Nearer the source lesser the losses, Construction cost and maintenance cost.
Source of water selected should be free from conflict or dispute or the dispute should be managed.