BILL Gates was right: toilets can show the quality of a nation. The richest man in the world spends a lot of time traveling to poor countries in Africa and Asia just to hang out in the toilets. For Gates, a country’s problems can be seen from the condition of its toilets.

He showed gigantic numbers: 2.5 billion—almost a third—of the world’s population lack access to a proper toilet. Because of poor-quality toilets, 5