Irrigation efficiency is the relationship or percentage between the volume of water actually used by the plants and the volume of water withdrawn at the intake.

Of the volume of water withdrawn at the inlet of an irrigation system, an important part is not used by the plants. The "losses" can be:

The theoretical volume of water to be supplied to the soil is that necessary to wet a uniform layer of soil, of a thickness equivalent to the average depth of the roots, in that phase of plant growth.