Base demographic data on cities were taken from GRUMP (4, 31). GRUMP urban extents are spatially defined primarily on the basis of satellite imagery of night-time lights. The extents are then linked with information from censuses and gazetteers containing population information on hundreds of thousands of urban settlements, including those with quite small populations. The algorithm that defines urban extents, especially for large urban agglomerations, typically gathers contiguous urban and suburban areas into one urban extent. For our study, we evaluated the water availability and population for the entire urban extent as measured by GRUMP; this assumes water sharing among constituent municipalities that may or may not occur in practice.