Earlier this year, an obscure United Nations document, the World Water Development Report, unexpectedly made headlines around the world. The report made the startling claim that the world would face a 40 percent shortfall in freshwater in as soon as 15 years. Crops would fail. Businesses dependent on water would fail. Illness would spread. A financial crash was likely, as was deepening poverty for those just getting by.

The U.N. also concluded that the forces destroying the world’s freshwater supply were not strictly meteorological, but largely the result of human activity. That means that with some changes in how water is managed, there is still time—very little, but enough—for children born this year to graduate from high school with the same access to clean water their parents enjoyed.

Though the U.N. looked at the issue across the globe, the solutions it recommended—capturing rainwater, recycling wastewater, improving sewage and plumbing, and more—need to be implemented locally. Some of the greatest challenges will come in cities, where bursting populations strain systems designed to supply far fewer people and much of the clean water available is lost to waste and shoddy, centuries-old infrastructure.

We’ve looked at eight cities facing different though representative challenges. The […]