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close this book Using water efficiently - Technological options
close this folder Water use efficiency
View the document What efficiency are we talking about?
View the document What are current levels of water use efficiency in irrigation?
View the document Factors affecting irrigation water use efficiency
View the document Water use efficiency in the urban sector: Definitions
View the document Factors affecting urban water use efficiency: Examples

What efficiency are we talking about?

The word 'efficiency' relates outputs to inputs, and has different meanings in different contexts. In economics, efficiency usually relates financial (or adjusted financial) returns from water use to the cost of water supplies. In agronomy, efficiency relates the ratio of the volume of goods produced to the amount of water consumed.

In this paper, the concept under discussion is technical water use efficiency. It is the relationship between the amount of water required for a particular purpose and the quantity of water delivered. It is an important measure to guide conservation efforts for water resources. In addition, the effectiveness of water delivery can be another measure to evaluate the timeliness of supply, quantity, equity in allocation, and the quality of water. However, this concept of effectiveness is not covered in this paper.

The technical efficiency criterion can be applied to different levels of water use, depending on how physical boundaries are defined. For instance, it can refer to a distribution system, a manufacturing enterprise, a field or an individual farm, a project area, a basin, or a sector. Debates about 'water use efficiency' are often based on an inadequate understanding and inconsistent use of the term 'efficiency'. In some cases, this confusion has led to faulty investment strategies, policies and actions.

The next section reviews the definitions of water use efficiency at various levels within different sectors. It then uses examples to illustrate the issues that are involved in evaluating WUE.