RIVERSIDE, Calif. — Dogs are well-known for slaking their thirst at the porcelain bowl. So how would you feel about drinking toilet water? If your response is a resounding “yuck!” you might be surprised to know that a reclaimed version, known as recycled wastewater, is already in use in some water systems.
The health and safety of drinking recycled wastewater is no longer in question. What about the taste? Researchers at the University of California, Riverside, decided to test the waters, so to speak, by pitting recycled wastewater against tap and bottled water in a blind taste test.
Water shortages and droughts in California have helped consumers get more accustomed to the idea of adding recycled water to the dwindling supply of conventional groundwater. Nevertheless, they were not fooled by the “recycled” label. Some came up with a more clever moniker: “toilet to tap.”
“It seems that this term (wastewater), and the idea of recycled water in general, evokes disgust reactions,” says Daniel Harmon, a graduate student in psychology at the university and the lead study author, in a university release. “It is important to make recycled water less scary to people who are concerned about it, as it is an important source of water now and in the future.”
Reverse osmosis is the process used to make wastewater reusable. Indirect potable reuse (IDR) allows the virtually contaminant-free treated wastewater to be reintroduced into groundwater supplies and eventually recycled into drinking water. IDR is already in use in a half-dozen California water systems, including the city of Los Angeles.
For the blind taste test, 143 participants were asked to rank the taste of water samples on a scale of one to five. The water samples, presented in similar cups and unlabeled, included IDR-treated tap water, conventional tap water and commercially bottled water. Similar to a wine tasting, testers also considered other elements of the “bouquet” — texture, temperature, smell and color.
As part of the study, researchers considered the participants’ genetic predisposition to taste differences. People who are more taste sensitive, for example, will detect bitterness in paper strips coated with the chemical phenylthiocarbamide (PTC). Researchers also factored in personality traits that make people either open to new experiences or anxious and insecure about trying new things.
Although the researchers hypothesized that all three water sources would score equally, one surprisingly stood out as least favorite.
“The groundwater-based water was not as well liked as IDR or bottled water,” says Mary Gauvain, a professor of psychology at the university and study co-author. “We think that happened because IDR and bottled water go through remarkably similar treatment processes, so they have low levels of the types of tastes people tend to dislike.”
Participants with nervous or anxious personalities liked the similar-tasting IDR and bottled water, but did not like the mineral-rich flavors of tap water. Those who had more open personalities liked all three samples equally well.
Researchers were surprised to find that women were twice as likely as men to prefer bottled water. They believe the study results indicate that women have a higher “disgust reaction” than men and are more expressive about what they dislike.
As a result of their study, researchers are optimistic about the future of recycled wastewater. Consumers used to drinking bottled water will find that water treated by reverse osmosis has a very similar palate. They suggest that marketing campaigns be aimed toward women, who make most purchasing decisions and show a willingness to try new experiences.
“We think this research will help us find out what factors people pay attention to in their water decisions, and what populations need to be persuaded to drink IDR water and how to persuade them,” concludes Harmon .
As for the disgust reaction, researchers plan to study the yuck factor in their next research project.
The full study was published in the February 2018 edition of the journal Appetite.