Competition between irrigation and domestic uses is usually decided in favor of the latter, because the economic willingness to pay is higher for domestic uses. The allocation of water in southern California, U.S.A., in recent years is an example. Table 1 Irrigation efficiency factors 1. Conveyance efficiency - ratio of water delivered to water diverted from source 2. Application efficiency - ratio of water reaching the soil to water delivered 3.
Water use efficiency - ratio of water available for the crop to water applied to the soil.
Efficiencies can be increased in different ways. Losses in distribution systems can be avoided by using pipes or by lining irrigation canals. Application efficiency varies with the irrigation system, and can be increased, for example, by changing from furrow to sprinkler or drip irrigation systems. Irrigation scheduling can be used to determine exact amounts of water needed by the crop. Table 2 shows a hypothetical example where different parts of a field hold different amounts of water in the root zone.