Drinking toilet water: The science (and psychology) of wastewater recycling

Would you drink water that came from a toilet? The imagery isn’t appealing. Even knowing that the water, once treated, may be cleaner than what comes out of most faucets, many people are disgusted by the idea. But in places like Singapore and Namibia, limited supplies of freshwater are being augmented by adding highly treated wastewater to their drinking water. As climate change and population growth strain freshwater resources, such strategies are likely to become more common around the world, and in the United States.

A Limited Resource

Freshwater is a more precious commodity than many people in the developed world recognize. More than 97 percent of Earth’s water is saline, unfit for drinking. Of the remainder, more than two-thirds is frozen in glaciers and icecaps, leaving just 1 percent of all the water on our planet fresh. About one one-hundredth of that 1 percent resides in lakes, rivers and other waterways; the rest is in aquifers beneath the surface or trapped in soil. It’s a wonder that so many of us take limitless, on-demand clean water for granted.

Pressure on this invaluable resource is growing. Over the last several decades, regional and local water shortages are becoming increasingly common. Australia saw the worst droughts in its settled history between 1995 and 2009. Droughts across the U.S. last summer crippled farm crops. And people are adding to that burden: Los Angeles, Las Vegas and Phoenix are located in some of the driest parts of the U.S.; they are also among the metro regions experiencing the highest rates of population growth.

Control of water resources is also a point of friction along already-contentious borders between Israel and Jordan, India and Pakistan, and Turkey and Syria, for example. And some experts think that water may supplant oil as a major spark of future conflicts.

“Water is becoming a geopolitical conflict,” says David Feldman, a political scientist at the University of California at Irvine. “When we talk about reclaimed wastewater, we’re not talking about something that’s simply at the level of convenience. We’re really dealing with an issue that is going to be affecting every country, every society.” Avoiding future clashes over water, he says, will mean having to drink treated wastewater.

With only a finite amount of water on the planet, chances are good that the water you drink passed through a person or animal at some point. More directly, many cities use rivers like the Colorado, Mississippi and Thames as their source for drinking water, while at the same time other cities upriver are discharging treated waste into them.

Down the Drain

Understanding the process of water treatment can help to make wastewater recycling more palatable, say scientists and activists working to promote its adoption. In most Western cities, when a person flushes a toilet, waste is carried by sewers to a municipal wastewater plant. There, large solid material is separated from liquid with grates or screens. In a settling tank, smaller solids fall out of solution while oils rise to the surface and are skimmed off. The wastewater next moves to an aeration tank, where microbes feed on the waste and break it down. After a final settling step, the clarified water is treated with ultraviolet light, chemicals like chlorine, or other processes to kill any remaining germs before the water is released back into the environment. Many of these steps are then repeated when water for consumption is drawn from the same river, lake or reservoir where the treated wastewater was released.

In essence, advocates of recycling wastewater for human consumption merely want to shorten this pathway, by reintroducing highly treated wastewater into water supplies without first depositing it in an intervening lake or river. Several cities around the world are already showing that it’s possible.
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