With an average rainfall of under 240milli-meters a year, Pakistan is one of the world'smost arid countries. The population and the economy areheavily dependent on an annual influx of water into theIndus river system that emanates from the neighboringcountries and is mostly derived from rainfall and snow-meltin the Himalayas. Throughout history, people have adapted tothe low and poorly distributed rainfall by either livingalong river banks or carefully husbanding and managing localwater resources. In the nineteenth century, the advent oflarge-scale irrigation technology decisively shifted thebalance between man and water. In the twentieth century,Pakistan faced several political and natural challenges toits water economy. There were successfully managed throughthe Indus water treaty with India and the shrewd applicationof science, technology, and economics, but Pakistan is onceagain facing a number of very serious water-related threatsto its survival.