In the 2015 sci-fi movie The Martian, an American botanist (played by Matt Damon) abandoned on Mars is forced to spend months in a small, enclosed “habitat” module. Combining high-tech hardware with Yankee ingenuity—spoiler alert!—he uses his bodily wastes to grow potatoes and purify water. The Martian offers a cinematic first: recycled urine and feces as a major plot element.
Far from science fiction, direct potable reuse (DPR) of highly treated recycled (reclaimed) water for drinking purposes, pejoratively termed “toilet to tap,” is fast becoming reality. The U.S. Environmental Protection Agency (USEPA) has dramatically revised its viewpoint: although its 2004 Guidelines for Water Reuse discouraged DPR, its 2012 reissuance concludes DPR is now “a reasonable option based on significant advances in treatment technology and monitoring methodology of the last decade.”
Case in point: Big Spring, Texas. In 2011, as severe drought dried up the town’s reservoir, it turned to a $13 million DPR facility to recycle 20 percent of its water. In 2014, a larger Texas town, Wichita Falls, followed suit.
On September 22, 2015, the Los Angeles Times reported that the Metropolitan Water District of Southern California, a massive water importer that serves Los Angeles, is talking to county sanitation districts in planning what could be one of the world’s largest DPR projects.
DPR has advantages over desalination, which requires far more energy to pump salt water through reverse-osmosis filters and to pipe intake water and brine discharge longer distances. And unlike desalination, DPR technology can be implemented at scales ranging from whole cities to neighborhoods to—potentially—as small as a single household.
To demonstrate the latter, engineering students at the University of Miami in Florida directed by Professor James Englehardt with a major grant from the National Science Foundation and the USEPA built and operated, from 2012 to 2014, a low-energy/low-emission DPR system for a four-bedroom “Net-Zero Water Dorm” using no city water.
In the students’ design, wastewater was passed through a series of physical, biological, and chemical treatment steps; to prevent mineral buildup, some water was then discharged into the sewer and combined with rainwater. The result met all potable water standards, eliminating all pharmaceuticals as well, but current regulations prohibited students from drinking or cooking with it.
Professor Englehardt’s focus is on nearly closed-loop standalone systems. He points out that such systems, by reusing hot water discharge, e.g., from sinks and showers, save more energy at the water heater than is consumed in the water treatment itself—in the United States, for example, up to 60 percent more.
DPR has regulatory, social, and environmental dimensions. First, and most obvious, is the need to overcome public perceptions about “drinking pee.” Regulatory changes may be required to allow human consumption. And the constraining role of water scarcity may diminish, resulting in development pressure on currently uninhabitable—and fragile—spaces. Luxury communities in remote deserts! Matt Damon’s space station on Mars may truly be a harbinger of terrestrial changes to come.