On a dusty hilltop in San Diego, the drinking water of the future courses through a wildly complicated and very loud jumble of tanks, pipes, and cylinders. Here at the North City Water Reclamation Plant, very not-drinkable wastewater is turned into a liquid so pure it would actually wreak havoc on your body if you imbibed it without further treatment.

First the system hits the wastewater with ozone, which destroys bacteria and viruses. Then it pumps the water through filters packed with coal granules that trap organic solids.