Business Week: With oil over $120 a barrel; prices for corn, wheat, copper, and steel close to record highs; carbon dioxide emissions causing climate change; and the world economy slowing, the last thing anyone needs is another crisis. Yet one is brewing now, in the U.S. and many other countries, where dwindling supplies of the world’s most precious commodity — fresh, potable water — threaten the health and welfare of billions of people. Already, 2.8 billion people — or 44% of the world’s …