[Vienna, 02 December, 2025] — A new study analyzing over 100 cities across Asia, Africa, and Latin America has quantified the stark consequences of urban sprawl on water and sanitation access, finding that how cities grow might determine whether hundreds of millions of people have access to these basic necessities.
The analysis, conducted by researchers at the Complexity Science Hub (CSH) and the World Bank, examined infrastructure data and economic indicators, including information on the footprint of 183 million buildings and 125,000 household surveys, to understand the relationship between urban form and access to clean water and sanitation.
The study modeled three scenarios for urban expansion (see Sidebar) and found that, if cities spread outward rather than building more densely, access to clean water and basic sanitation could be significantly impacted. "With horizontal growth, 220 million fewer people would have access to piped water and 190 million fewer would have access to sewage systems by 2050," points out Rafael Prieto-Curiel, lead author from CSH.
Distance From the City Center Matters
Cities that sprawl outward already face challenges, and the study quantified what many people already experience in cities like New Delhi, Cairo, Lagos, or Bogotá. Water bills are 75% higher in sprawling cities compared to compact ones, and access to piped water drops by 50% in more dispersed urban areas, according to the paper published in Nature Cities.
"In addition, residents in outer neighborhoods have 40% less access to critical infrastructure compared to those living closer to the city center", add the researchers.
Take a look at the interactive visualization " Urban Thirst" , created by CSH Liuhuaying Yang , and discover how urban form impacts water access and service costs in more than 100 cities in 55 countries.
Asia and Africa are in the Spotlight
Urban populations in Africa and Asia will grow substantially by 2050 (tripling and increasing by half, respectively), demanding considerable planning efforts. "African cities face particular challenges, with populations expected to surge from 550 million in 2018 to nearly 1.5 billion by 2050," point out the researchers. "African cities are already nearly twice as sprawling as Asian cities, with only 12% of residents living in central areas compared to 23% in Asia."
From Evidence to Action
"Water scarcity gets a lot of attention, but urban form is something we can actually control through planning and policy," says Prieto-Curiel. "Our analysis shows that effective planning can significantly enhance access to water and sanitation. Compact, walkable neighborhoods with adequate density aren't just environmentally sustainable. They ensure that basic services are available to everyone."
"Basically, our work shows that, by building cities better, we would be able to increase access to water and sanitation services. This can be done just by considering the shape of a city, no need to invest more money or build more infrastructure, but only considering the location of where that happens," adds Prieto-Curiell.
The researchers stress, however, that densification alone isn't a panacea; even some densely populated slums like Kibera in Nairobi, Rocinha in Rio de Janeiro, or those in Iztapalapa in Mexico City remain underserved. The research, however, shows that sprawling growth makes service delivery many times more difficult in cities.
Why city shape matters for water access
The team modelled three growth scenarios for cities doubling in size: compact (building denser and filling gaps), persistent (continuing current expansion patterns), and horizontal (spreading outward). "We assumed the only element that changed was where new development happens within the city," explains Prieto-Curiel.
To compare cities of varying sizes, the researchers measured how spread out each city is. They call this sparseness: basically, do most people live close to downtown, or are they scattered far from the center?
Cities with low sparseness concentrate most residents near the center. Jakarta, Indonesia, exemplifies this: more than half its 33 million residents live in central areas. Cities with high sparseness scatter populations across distant neighborhoods. In Kigali, Rwanda, only 15% of the 2.2 million residents live centrally, with most far from the core.
The researchers found that round, dense urban development could provide piped water to 220 million more people and sewage services to 190 million more than horizontal sprawl would. Persistent growth, maintaining current patterns, would keep access rates roughly stable. But horizontal sprawl would actively reduce the share of people with access to these basic services.
About the Study
The study "Urban sprawl is associated with reduced access and increased costs of water and sanitation," by Rafael Prieto-Curiel , Pavel Luengas-Sierra, and Christian Borja-Vega is published in Nature Cities (10.1038/s44284-025-00338-3).
About CSH
The Complexity Science Hub (CSH) is Europe's research center for the study of complex systems. We derive meaning from data from a range of disciplines – economics, medicine, ecology, and the social sciences – as a basis for actionable solutions for a better world. CSH members are Austrian Institute of Technology (AIT), BOKU University, Central European University (CEU), Graz University of Technology, Interdisciplinary Transformation University Austria (IT:U), Medical University of Vienna, TU Wien, University of Continuing Education Krems, Vetmeduni Vienna, Vienna University of Economics and Business, and Austrian Economic Chambers (WKO).
