New York Times: Laura Garcia was halfway through the breakfast dishes when the spigot went dry. The small white tank beneath the sink that purified her undrinkable water had run out. Still, as annoying as that was, it was an improvement over the days before Ms. Garcia got her water filter, when she had to do her dishes using water from five-gallon containers she bought at a local store. Ms. Garcias well water, like that of her neighbors, is laced with excessive nitrates, a pollutant associated with agriculture,...