What recycled sewage water reveals about human psychology

Posted on March 17, 2015

A few years ago Bill Gates teamed up with an engineer named Peter Janicki to create an ingenious machine that uses the same ingredient that taints water supplies - human waste - to clean them. The "Janicki Omniprocessor", which looks something like a miniature power plant, can turn waste from 100,000 people into 86,000 liters of clean water a day while generating enough electricity to power itself. "The water tasted as good as any I've had out of a bottle," Gates wrote on his blog. We know recycled water is clean, we trust the science, and it's exciting to think about how many lives it will save. And yet, that nasty "Yuk!" feeling persists.

Part of our deeply rooted aversion for tainted water has clear evolutionary origins. Like many animals, we instinctually avoid food and liquid that has touched nasty substances for health reasons. Think of this instinct as Paleolithic germ theory. It wasn’t exactly modern epidemiology, but for the most part, it worked.

Unfortunately, our instincts occasionally play tricks on our judgment. In a somewhat grotesque but captivating area of study, researchers have shown that people refuse to drink orange juice from unused urine collection bottles, eat soup served in a brand-new bedpan, or touch delicious fudge baked in the shape of dog feces. It’s as if there's some sort of immaterial essence that tarnishes these perfectly edible items.

This brings me to a new survey of over 2,600 Americans conducted by disgust guru Paul Rozin and his colleagues. Participants first read a short passage explaining how recycled water is certified safe and indicated their willingness to drink it. Next, they scored how comfortable they were drinking different types of water, from commercial bottled water, to tap water, to sewage water that had been boiled, evaporated, and condensed into pure water. Finally, they rated how comfortable they felt drinking recycled water if it had spent a certain amount of time in a reservoir or aquifer before it was fed back into the water supply.

The findings revealed something important about how the human mind perceives purity. Even though sewage water that is boiled, evaporated, and condensed is purer than tap water, participants overwhelmingly preferred tap water.

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Source material from British Psychological Society