The Tricky Task of Smelling and Tasting Drinking Water
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You walk inside on a hot day. You’re thirsty. You immediately head to the sink and fill a glass with tap water. You bring it to your lips, and experience the wonderful feeling of quenching thirst. “Wow,” you think, “this water tastes great.” It’s fresh and clean—it’s what water should taste like.
But what happens when the water doesn’t taste right? Just as we’ve all experienced how refreshing a glass of water can be, we’ve likely had an opposite experience. When you drink water with a poor flavor or smell, it can often be hard to place what’s making it unfavorable—it’s simply “wrong”.
Taste and odor issues in drinking water—also called aesthetic water quality issues—are usually brought to the attention of water utilities by their customers. However, when customers reach out to report an aesthetic water quality issue, it is often difficult for them to describe what’s wrong with their water. Many customers give little detail, claiming that their water tastes or smells different, unable to attach specific descriptors to their senses. Water utilities are interested in improving the dialogue between customers and their personnel, because it leads to quicker resolution of aesthetic issues while using less resources.
A young woman enjoys a refreshing glass of tap water. Credit: Aaron Whittemore.
The Virginia Tech Water INTERface Interdisciplinary Graduate Education Program (IGEP) team is tackling this problem by furthering the knowledge of taste and odor issues in drinking water and improving consumer-utility dialogue on aesthetic water quality issues. “We too often take tap water for granted,” says Andrea Dietrich, a professor in the Civil & Environmental Engineering Department at Virginia Tech and co-director of the Water INTERface IGEP. “Tap water is a valuable and healthy resource, and occasionally encounters an aesthetic issue. An interdisciplinary team approach is required to correct those issues and efficiently regain that clean, refreshing water we’re used to. Customers, engineers, and scientists are all on the team.” The first step to better resolving these issues is understanding why they’re difficult in the first place.
The complexities and difficulties of describing water taste and odor issues
The human senses are inherently complex. Our sense of taste is restricted to five distinct categories: sweet, sour, salty, bitter, and savory/umami. Most humans can readily differentiate between the five tastes, but individuals will vary in their ability to do so, and when combinations of taste are mixed, as in a beverage, it becomes more difficult to describe.
While there are only five distinct tastes, it is theorized humans can detect over one million distinct types of smell. Think about that for a second—if you smell something in your water, there are potentially one million different options for what you could be experiencing. Now think about narrowing those one million options down to a couple of words to describe what you’re sensing. That’s likely to be a daunting task for anyone.
Most people attempt to make this task easier by searching their memory for familiar flavors they have experienced in the past, and describing new sensory experiences based on the familiar. Some chemicals with familiar smells, such as hydrogen sulfide which gives off a “rotten egg” odor, are easy for people to identify and describe. However, tastes and odors in drinking water may be caused by chemicals that enter the water that are not familiar. Less familiar chemicals have a much more varied array of descriptors and are especially hard for consumers to describe.
Finally, even when consumers can identify a taste or odor and describe it, their terminology may be very different from one another. “People will use different words to describe the same experience. We need a common language to describe our senses in a useful way,” saysRenata Carneiro, a Virginia Tech doctoral student in the Food Science and Technology Department and Water INTERface IGEP fellow.
Gary Burlingame, the director of the Bureau of Laboratory Services for the Philadelphia Water Department (PWD), has direct working experience with these issues. In the 1990s, an algae that gave off a cucumber-like smell was affecting Philadelphia’s drinking water. Customers called in complaining of a wide range of smells, but most had little resemblance to cucumber. During a PWD learning event, six high school students were given a sample of the off-flavored water and asked to smell and describe the sample. Similar to PWD customers, most struggled to describe the odor. One student suggested that the sample smelled like cucumber, but the others disagreed saying that such a smell would not be found in tap water. Burlingame attributes this to consumer expectations. “People have expectations for what’s in a product. If it’s unusual, they have trouble describing it. No one expects their tap water to smell like cucumber.” Of course, that one student was correct. Because the cucumber smell is not associated with expected drinking water odors, the others had difficulty in acknowledging the cucumber smell and instead searched their memory for logical alternative descriptors.
Improving customer descriptions of water taste and odor through novel methods
After experiencing similar, recurring issues, the PWD partnered with Water INTERface researchers at Virginia Tech to find ways to help customers better describe taste and odor issues in their water.
The PWD determined there were 21 different chemicals of interest for drinking water taste and odor issues that could someday affect Philadelphia’s water. After identifying these chemicals, Burlingame collaborated with Virginia Tech and Dietrich to comb through hundreds of studies and resources to find common descriptors for the taste and odor of the 21 chemicals. Because chemicals had many and various descriptors from the multitude of sources, word clouds were generated to visualize the dominant and minor descriptors for each chemical. Some chemicals featured word clouds with many different descriptors, while others had one or few descriptors, representing the variation of consensus in different chemicals’ descriptors.
Word clouds for copper (left) and sodium (right) obtained from the literature review study. Credit: Andrea Dietrich.
After the descriptors for each of the 21 chemicals were compiled, a follow up study led by Renata Carneiro tested consumer’s ability to use the new descriptors to describe drinking water samples. The final 28 descriptors of the chemicals were placed in a check-if-apply list—a list of descriptors that can be checked if they apply to the experience of an individual.
An example of a check-if-apply list with common descriptors for drinking water samples. Credit: Aaron Whittemore.
In this study, the check-if-apply list was given to 75 adult volunteer subjects who evaluated seven drinking water samples by tasting them. One sample was pure bottled water, two were tap water, and the other four contained either tap water or bottled water with one of four different chemicals commonly found in drinking water and known to cause aesthetic water quality issues. Subjects were asked to taste each sample and then check the line by descriptors on the check-if-apply list that applied to that sample.
Renata Carneiro is shown here in the laboratory with a water sample ready for tasting. On the other side, a subject sits in a booth, waiting to receive the sample through the opening. Credit: Renata Carniero.
Subjects consistently checked different descriptors on the check-if-apply list for each of the different samples, showing that they identified different flavors between the samples. The vast majority of subjects also reported the check-if-apply list as “somewhat easy” to “very easy” to use. Carneiro attributes this to the simple structure of a list. “A list of words is easy for people to read and relate to,” she says. Virginia Tech researchers hope that utilities will begin making check-if-apply lists more accessible to customers. If customers can reference this simple list while identifying taste and odor issues in drinking water, it will likely lead to a quicker and more effective response in addressing the problem.
The PWD plans to implement the check-if-apply list into PWD protocol for handling aesthetic water quality issues. Currently, aesthetic water quality issues are usually identified by customers who then call the PWD to report the problem. Their trained staff ask questions to determine what may be causing the issue, hoping to identify a specific chemical or substance that may be the root cause before sending a staff member to test the customer’s water. Here, the check-if-apply list could help refine how PWD personnel ask questions. By referencing the check-if-apply list, staff could quickly narrow down a customer’s sensory experience to specific descriptors that may help to identify the possible chemical causes of the taste and odor issue. Using the list could significantly decrease the time spent addressing aesthetic water quality issues which would allow for more focus on other important issues of customer concern like monthly payments, water pipe issues, and more.
Check-if-apply lists are actually a simplified and focused version of a long-standing tool used by the professional drinking water industry—the Drinking Water Taste-and-Odor Wheel (T&O Wheel). The drinking water industry has been using the T&O Wheel as a reference for standardized descriptors for aesthetic water quality issues since its inception in the late 1980s. The T&O Wheel describes eight major categories of odor and four major categories of taste. These categories make up the innermost circle of the wheel and are related to a second circle that contains specific descriptive words associated with each category. Finally, the third and outermost circle associates the categories and their descriptors with one or more specific chemicals. This allows water industry professionals to communicate quickly with each other, even globally, about what chemicals may be in drinking water based on its taste or odor.
However, consumers do not usually have access to the T&O wheel when they notice an aesthetic water issue. Virginia Tech Food Science and Technology postdoctoral researcher, and former Water INTERface IGEP fellow, Katherine Phetxumphou thinks this should change.
Phetxumphou led a study that tested consumer’s ability to describe odorants with and without the use of the T&O Wheel. Study subjects were first asked to smell four different odorants that are commonly found in drinking water and record descriptions for each. Then, two months later, the subjects again sniffed and described each of the odorants. This time, however, they were briefly introduced to the T&O Wheel and were asked to use it to help them describe each odorant. The results were promising—subjects were better able to describe three of the four odorants when using the wheel. Furthermore, nearly all subjects reported that they preferred having the T&O wheel to assist them in identifying the odorants. “When you have a sensory tool available to you, it’s easier and more accurate for you to describe what you’re smelling,” Phetxumphou explains.
Both Virgina Tech Water INTERface IGEP researchers and the PWD acknowledge that granting customers access to the tools themselves could be especially helpful They would like to see tools like the T&O Wheel and check-if-apply lists sent out to customers via billing statements, emails, water quality reports, or even an app. Regardless of how customers are granted access to these tools, it is likely to improve consumer confidence in tap water and utility response in addressing aesthetic water quality issues. “The closer we can get to customers realizing there’s something in the water that shouldn’t be there, and describing it with relatable terms of smell and taste, the closer we are to getting these issues resolved efficiently and effectively,” says Burlingame.
Through their work, researchers from the Virginia Tech Water INTERface IGEP have identified descriptors that pertain to common chemicals known to cause drinking water taste and odor issues, tested the validity of tools that can be used to aid utility and customer description and response to such issues, and theorized ways that these tools could be used in the drinking water industry. This research makes important strides in the drinking water taste and odor field and serves as a great example of applicable, collaborative research that makes a difference. Dietrich noted that the drinking water community is an open community—it shares experiences and knowledge with other utilities around the country and around the world. Before long, the outcomes of Virginia Tech Water INTERface research could be spread far and wide. Perhaps you may even notice a check-if-apply list or T&O Wheel included in your next water utility bill or water quality report.
Improving aesthetic water quality is one of the many issues in our world that interdisciplinary research can help to solve. Burlingame said it best, “Yes there will be problems, but as long as we can work together to solve them, science advances, and people learn from it.”