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Can Toilet-to-Tap Overcome Yuck Factor?

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Courtesy of Fluence Corporation

UC Riverside researchers use a taste test for recycled wastewater

Much has been made of the “yuck factor” associated with drinking recycled wastewater, but Daniel Harmon, a University of California Riverside psychology graduate researcher, recently conducted an experiment to determine whether the yuck is only in our heads.

Harmon’s research question isn’t only an academic one in the American Southwest, Australia, Africa, the Mideast, and other parched regions. Countries around the world are facing major challenges in delivering a safe stream of potable drinking water to growing populations, and wastewater reuse is seen as an important solution. It’s less and less tenable to discard great volumes of wastewater, especially when existing technology can cost-effectively treat it to an even higher standard than consumers have come to expect from their tap water.

Direct and Indirect Potable Reuse

Recycled wastewater is used in two ways:

  • Direct potable reuse (DPR), which delivers recycled drinking water directly to consumers
  • Indirect potable use (IDR or IPR), which is when highly treated recycled water is mixed with surface water sources or underground water sources.

In California, with another major drought in its early stages, some large-scale aquifer recharge programs are already in use. One, the Orange County Water District’s plant in Fountain Valley, California, has even set a Guinness World Record for the most wastewater recycled to drinking water in 24 hours.

Even with six California water departments operating IDR programs, it’s still important to educate the public about water reuse to quell ambivalence about drinking recycled water. The science is clear: When wastewater that’s highly treated with reverse osmosis (RO) enters the ground, it then naturally continues to be purified in aquifers until it is virtually contaminant-free.

But, science aside, how does the water actually taste?

The IDR Taste Test Challenge

Beyond competitions for the best beer from reused wastewater, most research has focused on scientific measurements by hydrologists. The UC Riverside study, however, was a blind taste test by a psychologist, and the results are in: Water from indirect potable reuse was favored over natural groundwater, with favorability ratings similar to those of bottled water.

One hundred forty-three subjects compared treated IDR tap water with regular tap water and retail bottled water, all in unmarked cups. Subjects graded the samples on a five-point scale for flavor, temperature, texture, color, and smell. The study design also considered other factors that can sway taste perception, such as sex, genetics, and personality traits like neuroticism (anxiety and insecurity) and openness to experience (receptivity to new things and variety).

Initially, the research team expected the ratings for each water sample to match, but most participants preferred both IDR and bottled water to standard tap water from natural groundwater. The researchers explained the similarity was probably due to similar treatment methods.

Interestingly, the subjects with neuroticism tipped the balance toward IDR and bottled water. The openness to experience subjects, however, had no preference. Twice as many women preferred bottled water. Researchers explain that women experience greater disgust reactions than men, so their reaction to flavors they dislike are more pronounced, perhaps accounting for the sex differential.

The researchers noted that comparisons of reverse osmosis IDR water and bottled water might ameliorate the common yuck factor. They suggested marketing should focus on similarities to bottled water.

While indirect potable water reuse has arrived, public education and acceptance has lagged. The UC Riverside study may have hit upon a novel solution: Cater to the public taste.

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