This story is part of What Happens Next, our complete guide to understanding the future. Read more predictions about the Future of Water.
When the ancient Romans built their first aqueduct, they set into motion an enduring idea: A modern city needs to build infrastructure that pumps water over, through, and around mountain ranges. Most of today’s cities route this water through massive treatment plants before distributing it to our homes through a maze of underground pipes. When we’re done using it, we pipe wastewater to treatment plants that release so much liquid into our rivers that treated sewage frequently accounts for the majority of the flow.
The water infrastructure that modern cities rely upon is not cheap. City leaders in North America, Europe, and Australia are scraping together funds needed to renovate aging mid-20th-century water systems; public utilities in the US spend nearly $110 billion a year on water and wastewater services. Meanwhile, their counterparts in the developing world are contemplating plans to replicate the infrastructure of the world’s wealthy cities, which they too may not be able to maintain in the long run.