Urban Sprawl Puts Clean Water Access At Risk

By 2050, the way cities spread out could leave hundreds of millions of people without basic water and sanitation.

A new analysis in Nature Cities, led by the Complexity Science Hub in Vienna and the World Bank, estimates that loose, outward growth could mean 220 million fewer people with piped water and 190 million fewer with sewage service compared with denser, more compact development. The work leans on an unusually detailed picture of how more than 100 cities in Asia, Africa, and Latin America are actually built on the ground, from 183 million building footprints to over 125,000 household surveys.

Many of those cities are already juggling rapid growth, climate shocks, and tight water budgets. Yet they keep pushing housing into far-flung, low-density neighborhoods where pipes, pumps, and treatment plants are expensive to build and hard to maintain. The new study argues that city shape is not just an aesthetic choice; it quietly decides who gets clean water from a tap and who does not.

What The Researchers Looked At

The team, led by data scientist Rafael Prieto-Curiel at the Complexity Science Hub, started with a basic question: how far are people from the center of their city, and how scattered are they overall? They defined “remoteness” as a standardized distance from a manually chosen city center, and “sparseness” as a population‑weighted average of that remoteness across each city. In places like Jakarta, a huge share of residents still live fairly close in; in Kigali, with far fewer people overall, most residents are spread across distant neighborhoods.

On top of that skeleton they layered in other data: local income estimates, a global index of “critical infrastructure” such as roads and power lines, and Demographic and Health Surveys that record whether households have piped water or sewage connections. A simple pattern appeared quickly. Central areas tend to be wealthier, denser, and better served; the outer belts are poorer, less built up, and further from almost everything. In African cities, only about 12 percent of residents live in the central zone, compared with roughly 23 percent in Asian cities, highlighting just how sprawled many African urban areas already are.

“We find that less remote areas have higher average income, are closer to critical infrastructure and have higher access to sewage and piped water,” the authors write.

Household data sharpen that picture. In Latin American cities, the study finds that roughly three‑quarters of households in the center have piped water, while the share falls to close to half in the most distant rings. In Asian cities, central households are several times more likely to be linked to sewers than those on the edge. At the whole‑city level, sparseness comes with a price tag: cities that are twice as sparse have, on average, water tariffs about 75 percent higher, weaker proximity to infrastructure, and roughly half the access to piped water.

Three Ways A City Can Grow

To see what this might mean for the future, the team imagined each city doubling in population under three simple growth styles. In a “compact” scenario, new buildings mostly fill gaps and thicken up closer-in neighborhoods. In a “persistent” one, cities keep expanding more or less as they do now. And in a “horizontal” scenario, new development stretches outward in relatively thin, far‑flung layers. The water supply, climate, and technology are held constant in these scenarios; the only thing that moves is where people live.

That small change turns out to matter a lot. Under compact growth, the model suggests, piped water could reach around 220 million more people by 2050 than under horizontal sprawl, and sewage service could reach about 190 million more. The stakes are especially high in Africa, where the urban population is expected to jump from roughly 550 million people in 2018 to nearly 1.5 billion by mid‑century. In those cities, compact growth nudges the share of residents with sewage connections up; sprawling growth pushes it down, even as the total number of city dwellers soars.

“Our analysis shows that effective planning can significantly enhance access to water and sanitation,” Prieto-Curiel said. “Compact, walkable neighborhoods with adequate density aren’t just environmentally sustainable. They ensure that basic services are available to everyone.”

Density, though, is not magic. The authors point to famous high‑density neighborhoods like Kibera in Nairobi or Rocinha in Rio de Janeiro that remain badly underserved despite being close to the urban core. Their point is not that crowding alone solves water access, but that layering sprawl on top of existing inequality makes service delivery much harder and more expensive. For a feel of how this looks city by city, the team built an interactive map, Urban Thirst, which lets readers explore how rainfall, water stress, and urban form line up in more than 100 cities.

What It Means For Planners

The study treats urban form as a missing piece in the global water conversation. Climate change, population growth, and rising per‑capita use are all well-known drivers of water stress. Where new neighborhoods are allowed to sprout, and how connected they are to existing networks, is much more squarely in the hands of planners and local governments.

For city officials, the results point toward familiar but often difficult choices: guiding more growth into infill and mixed‑use areas; protecting key watersheds from unchecked expansion; and making sure land‑use plans and water‑utility investments talk to each other rather than pulling in opposite directions. Development banks and UN agencies already publish playbooks on urban water and sanitation; this work gives those playbooks some new numbers on how much is at stake when cities spread out.

The authors end on a cautious note. Compact growth without investment or fair governance can simply mean more people packed into places that still lack safe pipes, drains, and treatment. And even the best‑planned cities will be working within real limits on freshwater and money. Still, their message is blunt: if cities are going to double in size, doing it in a tighter, more connected way can put basic water and sanitation within reach for tens of millions of people who might otherwise be left dry.

Nature Cities study