Namibia's capital Windhoek faces a challenge that many fast-growing citiesmay soon confront: How do you secure more water when there is almost none to spare?

In one of the driest regions of Sub-Saharan Africa, every drop counts. That necessity led Windhoek to become the first city in the world, back in the 1960s, to turn treated wastewater directly into drinking water, a system that today supplies more than a third of the city's water needs.

The city built in an arid climate is combining pioneering water recycling, underground water storage, and community-led conservation to cope with chronic water scarcity. What lessons can other water-stressed cities learn from a place where wasting water simply isn't an option?