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Introduction 11 l'\) o o w resource development in the Upper Basin and resulting slowing of economic growth, Another and more important factor is the heavy Colorado River runoff heginning in 1983 which purged significant amounts of salt from the reservoirs and further reduced salinity through dilution, This salinity improvement, while not permanent, is expected to persist for several years. . Since 1976, greater attcntion has heen given to the blending of Colorado River water with other waters to achieve more desirable salinity levels for M&I uses (notably in the Metropolitan Water Dis- trict of Southern California [MWD] service area) and to reclamation of wastewater for reuse in industry, landscape irrigation, or in groundwater recharge, Currently, the extent of blended water supplies also is sub- ject to the cost of power for pumping. The economic impacts of various sa~nity levels on the costs of blending water or treating it for reuse have not been dealt with to the desired degrce in the earlier research. For allthc.se rea./mos, it appeared timely to update and supplement the data appearing in the Kleinman and Brown report so that credIble and defensible estimates of current and future benefits of salinity control can be developed, with as much accuracy as the data permit. By developing a flexible, yet manageable computer program (a program suitable for use in an IBM- compatible personal computer adequate for computer graphics), future estimates of the eco- nomic impacts of salinity control can be done easily and swiftly. The program will permit ready modification of input parameters, e.g., salinity (TDS) levels, changes in crop values and in agricultural acreage planted. Moreover, shifts in water use from agriculture to M&J; changes in damage threshold levels; shifts in location of use that will occur as the Central Arizona Project matures and population changes; ch";l'- ges in discount rate; changes in costs of applian- ces, treatment processes, etc., all can be accounted for in the program, The Rationale for Defining Salinity Damages Earlier attempts to measure the effects of salinity have treated such effects as absolute: That is, the physical effects of salinity lcvels In reducing crop yields, in corroding and thus reducing the useful life of water-using household devices, etc., have been measured against an "ideal" salinity level at which no physical effect is apparent. Then these physical effects arc described in economic terms, such as the value of reduced crop production and the monetary costs of more frequent replaccment of washing machines, household piping, etc, Such an approach can be misleading, This measurement of physical and economic effects of salinity in water supply against an ideal water supply appears to have bcen taken with little justification. It may rcnect mcrcly the researchers' belief or assumption that saline water has deleterious effects which logically should be measured against a standard of pris- tine water whose salinity level is below the threshold that causes measurable effects, However, such pristine water is not always found in nature and certainly is rarely found in waters that have been subjected to the impacts of human activity. Salinity Effects vs. Salinity Damages There is a fundamental question undcrlying this study, a question whose answer has a major innuence on the study findings, yet one that can- not be answered solely through enginccring or economic analysis. That is, which physical and economic effects of saline water should bc termed "damages"? The answer is not provided (rom engineering, economics, chemistry or biol- ogy. There are philosophic aspects to considcr. For example, the term Udamage" carries with it the concept of mitigation. Rationality leads us to take steps to reduce or othelWisc correct damages, particularly those which are caused by man's action or inaction, and which can be con- trolled or corrected at a cost that is less than thc resulting benefit. Yet, merely because water is saline, it is not always appropriate to consider it as a source of damage.