India is basically an agricultural country, and all its resources depend on the agricultural output. Water is evidently the most vital element in the plant life. Water is normally supplied to the plants by nature through rains. However, the total rainfall in a particular area may be either insufficient, or ill-timed. In order to get maximum yield, it is essential to supply the optimum quantity of water, and to maintain correct timing of water, this is possible only through a systematic irrigation system. Thus, the necessity of irrigation is as follows:

1. Less Rainfall

When the total rainfall is less than needed for the crop, artificial supply is necessary. In such case, irrigation works may be constructed at a place where more water is available, and then to convey the water to the area where there is deficiency of water. Rajasthan canal is one such example. It conveys water to the arid zones of Rajasthan, where the annual rainfall is hardly 100-200 mm.

2. Non-uniform Rainfall

The rainfall in a particular area may not be uniform over the crop period. During the early periods of the crops, rains may be there, but no rainwater may be available at the end, with the result that either the yield may be less, or the crop may die altogether. By collection of water during the excess rainfall period, water may be supplied to the crop during the period when there may be no rainfall. Most of the irrigation projects in India are based on this premise.

3. Growing a number of crops during a year

The rainfall in an area may be sufficient to raise only one type of crop during the rainy season (i.e. Kharif crops), for which no irrigation may be required. However, with the provision of irrigation facilities in that area, crops can be raised in other season also (i.e. Rabi crops).

4. Growing perennial crops

Perennial crops such as sugar cane etc, which need water throughout the year, can be raised only through the provision of irrigation facilities in the area.

5. Commercial crop with additional water

The rainfall in a particular area may be sufficient to raise usual crops, but more water may be necessary for raising commercial and cash crops.

6. Controlled water supply

By construction of proper distribution system, the yield of the crop may be increased because of controlled supply of water.