Can people tell the difference between bottled water and tap water?

One of the funniest papers I have ever read is Can People Distinguish Pâté from Dog Food? (ungated earlier version here). The answer was no, people can't tell the difference. And it turns out that isn't the only example where people can't tell the difference. For example, in blind taste tests most people can't tell the difference between Coke and Pepsi (see here for more on that).

On a related note, this 2018 article (ungated here) by Kevin Capehart (California State University) and Elena Berg (American University of Paris), published in the Journal of Wine Economics (yes, there is such a journal), presents the results of a blind taste test of water. Capehart and Berg ran three experiments with 188 research participants (who were undergraduates at the American University of Paris). First, they gave their participants a brief training in water tasting based on a video of a water sommelier. And yes, there is such an occupation - see here:

Anyway, after their training, the research participants completed the three experiments. In the first experiment, they were given four sets of three glasses of water. Each set contained two glasses of the same bottled water, and one that was different. The research participants' task was to identify the glass that was different. How did they do? Capehart and Berg note that:

Although our subjects were better than chance at identifying the singletons, the singleton was correctly identified less than half of the time for each triangle test, including the last test with the biggest [total dissolved solids] difference... Moreover, our subjects correctly identified the singleton in less than half of the triangle tests—about 1.8 out of the four—on average... Those results suggest our subjects were only slightly better than chance at distinguishing bottled waters.

Ok, so far so not good. In the second experiment, the research participants were given five glasses of water - the same four bottle water types from the first experiment, plus tap water. They were asked to rate each water on a 14-point scale, and to rank them from best to worst. What happened? Capehart and Berg note that:

The Fiji brand of bottled water was given the most first-place rankings with a quarter of participants ranking it as their most preferred. Tap water was given the most last-place rankings with 29% ranking it as their least preferred. However, a quarter of participants also said that Fiji was their least preferred, and almost 20% said that tap water was their most preferred. Thus, there is no clear consensus about which waters are preferable to others.

And, in case you thought that the price of bottled water is a signal of quality, if you exclude tap water (which has a price of nearly zero):

...there is no correlation or perhaps even a negative correlation between the price of a bottled water and its rating.

Finally, in the third experiment, participants were given the same five water samples (randomised in order of course), and five descriptions. Four of the descriptions were taken from the water menu at Ray’s and Stark Bar in Los Angeles, and the fifth was simply "tap water". Their task was to match the descriptions with the samples. How did they do? Capehart and Berg note that:

For each water, the participants were not significantly better than chance at matching the water to its description, except for Acqua Panna, but even in that case, less than 30% of participants were able to correctly match it to its description.

The fact that only 24% of participants correctly identified the tap water also means that 76% mistook a bottled water for tap water. Speyside Glenlivet, Hildon, Acqua Panna, and Fiji were mistaken for tap 28%, 27%, 24%, and 18% of the time, respectively.

What do we learn from this? People can't really tell bottled water and tap water apart. If someone buys expensive bottled water, they are engaging in some conspicuous consumption rather than genuinely purchasing a higher quality product. As Capehart and Berg conclude:

Just as there is more to a wine than the look, smell, or taste of what is inside its bottle, there must be more to bottled waters than what is inside, especially since there are no visual differences among still waters, no odor differences, and subtle or non-existent taste differences. Consumers’ willingness to pay for an expensive bottled water must be rooted in other aspects besides the taste of the water inside it.