From Wired (Matt Simon):
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. Next, the water passes through fine membranes that snag any remaining solids and microbes. “The pores are so small, you can’t see them except with a really powerful microscope,” says Amy Dorman, deputy director of Pure Water San Diego, the city’s initiative to reduce its reliance on water imported from afar. “Basically, they only allow the water molecules to get through.”
But to be extra sure, the next step blasts the water with UV light, to obliterate any microbes and other trace contaminants. The end result is water in its purest form—too pure, in fact. The last phase is “conditioning” the liquid by adding minerals back to it. Without that, the water would leach the copper out of pipes. If you drank it, it’d soak up your electrolytes like a sponge.
If that all sounds like a rather convoluted way to get drinking water, that’s because the American West is facing a rather convoluted climate crisis. San Diego—and the rest of Southern California—have historically relied on water from Northern California and the Colorado River. But they’ve always been at the end of the line. The river hydrates 40 million other people in Colorado, Wyoming, Utah, Arizona, Nevada, and New Mexico, and it is withering under a historic drought, a harbinger of even worse water scarcity to come as the climate warms.
So San Diego has to figure out how to do more with less water. The Pure Water program aims to provide more than 40 percent of the city’s water from local sources by the year 2035 by reusing water recycled from homes and businesses. (That means water that has flowed through sinks, showers, toilets, and washing machines.) “We’re diversifying the portfolio,” says Todd Gloria, San Diego’s mayor. “We’re heavily dependent upon water that comes from very far away, and that’s a problem that we have to address.”
The water-recycling revolution is just getting going in San Diego, but its proponents hope it will ripple across the American West. In June, legislators in the US House of Representatives introduced a bill that would funnel $750 million into water recycling projects in 17 western states through 2027. (The bill hasn’t made it past committee.) “This is beginning to be our new normal—88 percent of the West is under some degree of drought,” Representative Susie Lee (D-Nevada) told WIRED in July. “Lake Mead is at the lowest level it has been at since the Hoover Dam was constructed. And the Colorado River has been in a drought for more than two decades.”
The technology to recycle water on a large scale already exists—it’s been around for half a century, in fact. But the problem is that it can cost billions to build a recycling facility, and you can’t just copy-paste a particular plan from one municipality to the next. The North City Water Reclamation Plant has been experimenting with different kinds of filtering membranes because not all water is the same. For example, the mineral content of the water flowing into the San Diego facility is distinct from what operators might be working with in New York. Recycling plants also cost a pretty penny to run, since pumping lots of water through fine membranes requires significant pressure. But then again, it also takes a lot of energy to pump water from northern areas to Southern California.