Google is using toilet water to cool its data center in western Georgia.

In 2007, when Google first opened its massive computing center in Douglas County, Georgia, it cooled the facility's equipment using the same water that's pumped into the pipes of local homes. But at some point, the search giant realized that the water used by its evaporative cooling system needn't be clean enough to drink.

On Thursday, Google revealed that it's now working with the Douglasville-Douglas County Water and Sewer Authority to cool the facility with 100 percent recycled water. "When the residents of the county take showers and flush their toilets, they're helping to cool our data center," Joe Kava, the man who runs Google's data center operations and construction team, tells Wired.

The company may save some money in the long term with its recycled water. But according to Kava, that's not the primary aim. In partnering with the Sewer Authority, Google is no longer putting the same strain on the area's natural water supply—and it's making sure it can ride out a drought. "The finances make sense, but over a much longer period of time. It was really about being environmentally responsible and securing our supply if there was rationing of potable water," Kava says. "You don't want to contribute to any fresh water shortage."

Google uses a similar system at its data center in Saint-Ghislain, Belgium—where it reuses water from a nearby industrial canal—and both efforts are part of larger movement toward "free cooling." In using local water and outside air to cool data centers, companies such as Google, Facebook, and Microsoft can reduce their dependency on power-hungry mechanical chillers. Like Google, these companies say they do this to reduce the damage that their massive computing facilities do to the planet.

The Douglasville-Douglas County Water and Sewer Authority (WSA) operates a water treatment plant that, yes, scrubs sewer water from local houses and returns it to Georgia's Chattahoochee River. But according to Google, the WSA is now diverting about 30 percent of that sewer water to a second treatment plant built and paid for Google. After it's cleaned at this second facility—which sits about five miles west of the WSA plant—the water is streamed to the company's data center.

The water is then used to run the data center's evaporative cooling system. Basically, Google pushes hot air from its servers into the much cooler water, and most of this water is then evaporated into the Georgia air as it cascades down large cooling towers. Any remaining water is moved into another treatment plant, where Google disinfects it, removes various minerals, and returns it to the Chattahoochee.

According to Michael Patton, the deputy director of water and waste water operations for the WSA, Google's setup does indeed remove a significant burden from the county's natural water supply. Google turned on its treatment center on in December 2008, Patton says, and the following summer—peak water season—there was an enormous drop in consumption across the system.

"It's a win-win for both us," Patton tells Wired, "and for the community too."

Google still operates some sort of electrical cooling system in the data center—the company won't go into detail, reluctant to reveal its "secret sauce"—but this is only used on days when the sewer water is too hot to cool the machines. "There is some chiller capacity here, but certainly not enough to run the entire facility on chillers," says Kava. "They're just used for what we call ‘heat shaving.' During those certain hours of the years when cooling towers by themselves are not sufficient, we can turn the chillers on." In Georgia, he says, these are only needed for a few hours in the middle of hot summer days.

In Belgium, where the climate is much cooler, Google can operate its data center without any chillers at all, and the same goes for its facility on the southern coast of Finland, where it cools servers using water from the Baltic Sea.

Microsoft and Facebook are also running data centers sans chillers. But methods vary. At its new center in Prineville, Oregon, for instance, Facebook cools its server room using the outside air coming off the high desert.

Old-school data center players have long used free cooling as well. At one of its "co-location" data centers in San Jose, California—a place where myriad businesses operate servers—Equinix uses the outside air to cool its server rooms, though it still relies heavily on chillers as well. According to Jerry Collier, senior director of International Business Exchange (IBX) operations at Equinix, the company can only embrace so much free cooling because many of its customers still insist that their servers run at extremely low temperatures.

Traditionally, data centers operate at temperatures between about 60 and 80 degrees Fahrenheit, but Google and others have realized that computing hardware can reliably run at much higher temperatures. This has opened the door to much more extensive free cooling—while putting a whole new spin on the flushing toilet.