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The water we flush will be the water we drink

By Zoë Schlanger
Published Last updated This article is more than 2 years old.

Today, an estimated 3.6 billion people live in places where access to water isn’t guaranteed for at least one month every year, according to a UN report released in 2018. This problem is not going to get better in the future: The world’s population is expected to grow by another 3 billion people by 2050, increasing water demand by a third. At the same time, climate change will have dried up some watersheds and caused contamination by flooding in others. The combination of population growth and diminished water access means that the number of people who don’t have a reliable water supply for at least a month per year could grow to as much as 5.7 billion.

But humans exist on a very short leash. A person can only last around three days without drinking water. In our very recent past, humans could afford to think of water as more or less a constant. Yes, drought hit, and other years brought flood, but eventually things returned to normal. But the next several decades (and indeed the decade we are currently living through) are a departure from the luxury of normal; water is undergoing a regime change. Drying reservoirs aren’t going to fill back up with the consistency we’ve come to count on. Water security will be one of the principal struggles of the modern era.

Wasting used water—by flushing it down the toilet or sink, to be discharged into rivers and into undrinkable oceans—might be inconceivably irresponsible. A closed-loop water system, in which we drink water, expel it, treat it and drink it again, might be the future. Indeed, in a handful of places around the world, it already is.

The technology to clean sewage to drinking water standards already exists. Can we get over our disgust reflex enough to try?

Astronauts do it

The science behind turning human waste into drinking water isn’t new. A high-tech version of direct potable reuse has been used by American astronauts since humans first left Earth. At the International Space Station, a high-tech water system on the US side collects astronauts’ urine, sweat, shower water, and even the condensate they breathe into the air. The mixture is spun in a centrifuge-like system until water vapor emerges, is recondensed, then heated, oxidized, and laced with iodine.

But drinking distilled urine is too much for the astronauts on the Russian side, who keep it separate from their purification system. But don’t worry, it isn’t wasted; US astronauts visit the Russian side of the ISS and pick up the urine, bring it back over to the American side, and add it to their purification system.

Toilet-to-tap: From Singapore to Namibia

Back on Earth, water engineers politely call wastewater recycling “direct potable reuse.” Others call it “toilet-to-tap.” In Namibia, the driest country in sub-Saharan Africa, the capital city of Windhoek has been turning raw sewage into drinking water for 50 years, and has never had a single illness attributed to the reclaimed wastewater.

Singapore has been doing it since 2003; It’s a natural choice for a country that lacks any native freshwater resources. “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. The government plans to squeeze a full 55% of its water supply from sewage by 2060.

The process on Earth is more rudimentary than in space, but it works; In some cases, waste is passed through membrane filters and exposed to UV light to kill bacteria. (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 filtration methods will have to keep evolving. Still, it’s a proven technology, and cost-effective at scale.

But beyond a handful of examples, cities and countries have been slow to adopt toilet-to-tap. The ick factor is still too much for most places, especially while the threat to their water supplies still remains a few decades away.

Next stop: Texas taps

Still, a change is coming, with a few particularly parched American towns and cities jumping aboard: Big Spring, Texas (population: 28,000) has been piping recycled sewage water to its inhabitants since 2014.

The border city of El Paso, Texas (population 700,000) is gearing up to do the same, but bigger. El Paso is incredibly dry. It averages a scant 10 inches of rainfall per year—drier even than Windhoek. They don’t really have a choice.

Over the last 30 years, the once-water-wasteful city underwent a reckoning; In 1985, each El Pasoan was using on average 205 gallons of water every day, far more than the US average of 112 gallons at the time. Water was cheap, and lush lawns were popular. But El Paso is in the desert, and that kind of water profligacy would soon prove a dangerous fantasy.

Water levels in the aquifer that quenched the booming border town were plummeting; they dropped 1.5 ft per year. A later report would reveal (paywall)that the aquifer level dropped a full 147 ft (45 meters) between 1940 and 1999. The city was on track to run out. Something had to be done.

Various water conservation measures began in 1991; water cops were hired to make sure people followed the rules, and water officials went to elementary schools to teach kids how to use less. Within 10 years, El Pasoans were using an average of 155 gallons per day each. By 2017, they were using 128. That’s still above the current national average of less than 100 gallons, but compared to other hot, dry places with roughly the same average rainfall—places like Fresno, California (240 gallons)—El Paso is a beacon of conservation. The water in the aquifer stabilized, and models developed at the time suggested the city would have a stable supply for at least the next century.

Having seen the brink, El Pasoans are used to the idea of having to experiment with new techniques to survive as a city; Toilet-to-tap is just another means for survival, ick factor be damned. The last time the city water utility polled their users, in 2016, 89% of respondents said they were ready and willing to drink direct potable reuse water.

The utility just completed a pilot project of the sewage recycler design, required by Texas state officials before the system could be cleared as safe. El Paso hopes to bring a plant online within the next decade. It will cost roughly $100 million (pdf)and be the biggest of its kind in the country.