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evaporation, evapotranspiration, or deep percolation to non-tributary aquifers, Likewise, the term "saved water" will be used to describe the larger increment of water produced by changes to historical diversion rates made possible with efficiency improvements, C, Methods of Improving Irrigation Efficiency An accepted measure of overall irrigation efficiency is the ratio of crop. consumptive use to gross headgate diversions, This efficiency can be improved by either reducing diversions or increasing crop consumptive use (or by a combination of both), Generally, the expanded use doctrine limits adding new consumptive uses to a decreed Colorado water right. In some circumstances, such as when an irrigator who historically has never had enough water to satisfy his l;rop needs becomes able to get more water to his existing acreage, increased consumptive use is allowed, Efficiency changes considered herein will focus on the more common means of increasing irrigation efficiency - reducing losses thereby reducing the diversion side of the efficiency ratio, Often, an increase in efficiency is endorsed as a reduction in "waste" without an attempt to define the term "waste", As already shown, non-consumptive losses generate return flows which are used by others and such water is not necessarily wasted, While frequently an increase in irrigation efficiency is promoted as conserving water supplies and in the public interest, such generalities fail to recognize the intricate movement of water within an irrigated region, Further, it is tempting to classify conveyance losses as non-beneficial uses of water, but, in fact, such water actually serves the necessary and beneficial purpose of moving the remaining water to its place of need. It is only when the method of conveyance is not "reasonable and appropriate under reasonably efficient practices" that these losses should be characterized as "non-beneficial," Section 37-92-193(4), c.R.S, What "reasonably efficient practices" means is central to statements about the efficiency and waste involved in irrigation water use, A common understanding is that beneficial use is a flexible concept which tolerates whatever degree of "inefficiency" is present in the prevailing irrigation methods of an area, Courts will likely be reluctant to require innovations with private investment that force any advance beyond those prevailing methods, Likewise, the State Engineer can probably not require state-of-the-art irrigation systems in an effort to reduce irrigation water diversions, However, the legislature, as the best arbiter of public perceptions and desires, may be in better position to balance policy questions and decide to move water users towards more efficient practices, It can do so by providing incentives (funding or creating a marketable right as proposed in the salvage bills) or by regulating (i.e" by declaring which "reasonably efficient practices" are necessary or otherwise tightening the definition of beneficial use), Similar approaches have already been applied to municipal users, i.e., financial and technical assistance on the one hand and mandatory plumbing code revisions containing maximum fixture demands on the other, Absent regulation, current conditions give some incentives for irrigators to make improvements to their systems, Some of the reasons cited by irrigators who have made 6