Dhaka, Dec. 5 -- A new study warns that rapid urban growth could leave millions of people without access to clean water and sanitation by 2050. Experts say how cities expand and where new buildings are constructed will directly affect the health and daily lives of hundreds of millions of residents.

Researchers from the Complexity Science Hub in Vienna and the World Bank studied more than 100 cities across Africa, Asia, and Latin America. They analyzed data from 183 million buildings and 125,000 households to understand how urban expansion could impact water and sanitation services.

The study outlined three models for city growth by 2050: compact development, maintaining current patterns, and horizontal expansion into new areas. The repo...