They took a bucket of muddy, bacteria-laden water. Added a bit of white powder. Stirred. And within minutes, standing amid 100 refugees in war-torn Liberia, researchers from Johns Hopkins University had produced what seemed like a magic trick: Clear, drinkable water. "I couldn't believe it when I saw it," Hopkins researcher Shannon Doocy said of her work last year. "The people in Liberia couldn't believe it." The powder, developed by Procter & Gamble Co. with the federal Centers for Disease Control and Prevention, is now headed for its biggest test yet: the tsunami zone. Relief agencies, led by AmeriCares of...