Across maps of the arid West, expensive water pipelines are being plotted to meet the region's profound need for water. Among those under serious consideration are a 263-mile pipeline to bring eastern Nevada water to Las Vegas, southwestern Utah's 139-mile Lake Powell pipeline, and the 500-mile Flaming Gorge pipeline from Wyoming to Colorado. Each would cost billions of dollars. But what if there’s not enough demand for water to pay for these projects? This might seem like an implausible question in a region defined by growth and expansion for over a century. But in fact, demand for water is falling in many parts of the country. Between the 1970s and the late 2000s, the amount of water used by American households fell everywhere -- by tens of thousands of gallons each year in Phoenix and Seattle, to nearly 100,000 gallons a year in Las Vegas. The trend is due to