Urban population can be usefully divided into three categories reflecting their perennial water shortage status (Table 1). A total of 162 million people will live in cities that will have perennial water shortage in 2050. The majority of people in this category will be in Asia (94 million), although Africa will have a greater percentage (7.7%) of total urban dwellers under perennial water shortage. A second category is people in cities that will not have perennial water shortage by 2050 at the 100-km buffer distance, but the buffer distance needed to avoid perennial water shortage will increase from 2000 to 2050. This potentially implies infrastructure investment to enable short-scale (