Public concerns about tap-water quality (and, let's face it, slick marketing) have caused bottled water sales to soar over the past couple of decades. Ads and labels drive home the perception of purity, with images of pristine glaciers and crystal-clear mountain springs. We now have "luxury" water bars and "premium" bottled water. Some people are spending 10,000 times more per gallon for bottled water than they typically are for tap. Is it worth the cost—to you and the environment?