Quality of Water in the Colorado River and the Yuma Desalting Plant
The federal government's activities to maintain deliveries to Mexico of Colorado River water of adequate quantity and quality have been haphazard and costly. Even the need for salinity control measures, such as the Yuma desalting plant, is a result of the government's lack of foresight about the effects that major storage works on the Colorado River and diversions of water from the river would have on the flows left to enter Mexico. As discussed in this chapter, purchase or lease of water from willing sellers would be one way to reduce the cost of operating the desalting plant.
The Colorado River Compact of 1922 recognized that the United States would have some responsibility for delivering water to Mexico, but left the quantity (and quality) unspecified. It did state, however, that in the case of a shortage, the Upper Basin and Lower Basin states would share the responsibility for making up the amount. The lack of a quantified international obligation left the Mexicali Valley in Mexico vulnerable to the depletions caused by water users in the United States (see figure 9-1). Frustration over this condition eventually led to the signing of the Mexican Water Treaty of 1944, which allotted to Mexico an average of 1.5 million-acre-feet of water annually. The treaty allowed some flexibility for the variable flow in the river since it specified that the 1.5-million-acre-foot amount had only to be met on average over a ten-year period; in other words, 15 million acre-feet of water had to be delivered every ten years. The treaty did not specify any quality parameters, although Mexico expected to receive water of a quality similar to that provided to Lower Basin users in the United States, such as the Imperial Irrigation District. Two events, however,