For much of the world, atlases no longer tell the truth. Today, dozens of the planet's greatest rivers run dry long before they reach the sea. They include the Nile in Egypt; the Yellow River in China; the Indus in Pakistan; the Rio Grande and Colorado in the US; the ancient Oxus that once poured into the Aral Sea in Central Asia; the Murray in Australia and the Jordan in the Middle East, which is emptied before it can even reach the country that bears its name. The dire state of such rivers is the most visible sign of a profound crisis in how the world uses its water - a crisis that reflects water's new place as one of the most important and threatened commodities. It's a situation that could herald a world in which wars are fought over water.