Treating brackish water is expensive, but it’s getting cheaper as the technology matures. In his work at the University of New Mexico, Hightower, the civil engineering professor, has been collecting data on desalination costs for decades. His research shows that in the US, starting in 2005, treating brackish groundwater from nearby sources has been less expensive on average than piping in fresh water from a remote source—especially if that source is 75 miles or more away, a common solution for arid places as their local supply of freshwater dwindles.
Texas is on it: the 2017 state water plan set a goal to turn 111,000 acre-feet of brackish groundwater a year into drinking water by 2070.
Water engineers politely call it “direct potable reuse.” Others call it “toilet-to-tap.” The United Nations calls it a massive untouched resource that could nudge society into a “circular economy,” where economic development is “balanced with the protection of natural resources…and where a cleaner and more sustainable economy has a positive effect on the water quality.”
In Singapore, an island nation lacking any freshwater resource big enough to sate its growing population (pdf), they’re a bit more direct: “Basically, you drink the water, you go to the toilet, you pee, and we collect it back and clean it,” George Madhavan, a director at Singapore’s public utility, told USA Today in 2015.
Since 2003, Singapore has been treating sewage to drinking-water standards. For now, most of that water is used for industrial purposes, but the volumes are impressive. About 40% of the nation’s total water needs are met by toilet-to-tap, significantly reducing the pressure on the rest of its freshwater sources—rainwater, desalinated seawater, and imports. In the last few years, the country started handing out bottles of the reclaimed water at events, to get its citizens used to the idea of drinking it directly. Singapore plans to squeeze a full 55% of its water supply from sewage by 2060. By then, they hope, drinking it will be the norm.
In Namibia, the driest country in sub-Saharan Africa, the capital city Windhoek has been doing “toilet-to-tap” for so long that several generations of residents don’t bat an eye at drinking the stuff. The city has been turning raw sewage into drinking water for 50 years. Windhoek has never had a single illness attributed to the reclaimed wastewater.
“Public confidence is that very, very fragile link that keeps the system going,” Pierre van Rensburg, Windhoek’s strategic executive for urban and transport planning, told the American Water Works Association, an international nonprofit, in 2017. “I think if there is ever one incident that could be linked back to the [direct potable reuse] plant, the public would lose all confidence.”
“It tastes like bottled water, as long as you can psychologically get past the point that it’s recycled urine.”
The science behind this isn’t new. In fact, a high-tech version of direct potable reuse has been used by American astronauts since humans first left Earth. In space, humans have no choice but to drink their own distilled urine. On the US side of the International Space Station, a high-tech water system collects astronauts’ urine, sweat, shower water, and even the condensate they breathe into the air, and then distills it all to drinking-water standards.
“It tastes like bottled water, as long as you can psychologically get past the point that it’s recycled urine and condensate,” Layne Carter, who manages the ISS’s water system out of the Marshall Flight Center in Alabama, told Bloomberg Businessweek (paywall) in 2015. The Russian astronauts, however, decline to include their urine in their water-purification system. So the US astronauts go over to the Russian side of the ISS and pick up their urine, bring it back over to the American side, and purify it. Water is precious, after all.
Back on Earth, the technology is more rudimentary. Whereas in space, urine is spun in a centrifuge-like system until water vapor emerges, is recondensed, then heated, oxidized, and laced with iodine, the process on Earth involves a combination of extracting waste through membrane filters and exposure to UV light to kill bacteria. (And in Namibia, they use waste-eating bacteria before zapping the microorganisms with UV.) To keep up with the ever-expanding number of chemicals and pharmaceuticals that show up in water, these water-reuse will have to keep evolving. Still, it’s proven technology, and cost-effective at scale.
Outside of a few examples, however, communities have been slow to adopt them as viable solutions to water scarcity, likely because of cultural stigma around drinking filtered sewage water. That’s slowly changing as rising temperatures, dwindling freshwater, and more frequent, more extreme droughts have cities looking around for options.