New York Times: The Southwest drought has reached the point where even drain water is coveted. Beginning nearly 40 years ago, the briny runoff from the “salad bowl” of southern Arizona, some of the most productive farmland in the nation, has been channeled into an arid plain of the Sonoran desert in Mexico. It is an engineered solution to the vexing problem of keeping the nearby Colorado River free of agricultural wastewater too heavy in salt compounds for drinking water and other uses. An …