Water is fast becoming one of the world’s most under-appreciated geopolitical fault lines.

New data from Watershed Investigations shows that 38 of the world’s 100 largest cities are located in regions of extreme water stress—where demand for public and industrial use is close to exceeding available supply. Around one billion people now live in major cities experiencing long-term drying trends, compared with just 100 million in regions becoming wetter.

From Los Angeles and Mexico City to Tehran, Karachi and Beijing, the map reveals a stark pattern: the world’s fastest-growing urban centres are often located in the most water-scarce regions. As climate change, pollution and mismanagement intensify pressure on freshwater systems, water scarcity is no longer just an environmental issue—it is a driver of economic instability, urban vulnerability and geopolitical competition.

In the decades ahead, access to water may shape power, migration and conflict as profoundly as energy or territory.