The quality of drinking water is critical to public health, yet many people may not realize that fungi play a significant role in affecting the taste and odor of their tap water. Fungi have long been an underappreciated factor in water contamination, and recent studies, like one published in Environmental Science & Technology, are exploring how these organisms can affect water quality. The study revealed that fungi contribute to taste and odor issues in drinking water by producing a range of odorants, many of which can create off-putting earthy or musty smells and tastes. While these aesthetic issues are annoying, the presence of fungi in drinking water can also have more serious health implications.
How fungi contribute to taste and odor issues
Fungi in water systems are not new, but they have often been overlooked as contributors to taste and odor problems in drinking water. According to the study, researchers identified 17 odorants produced by 10 native fungal isolates collected from drinking water treatment plants and plumbing systems. Among the fungal genera responsible for producing these odorants, Penicillium, Aspergillus, Paecilomyces, and Alternaria stood out as the most significant offenders. These fungi are capable of producing high yields of odor-causing compounds, including 2-methylisoborneol (2-MIB), geosmin, and 2-isobutyl-3-methoxy-pyrazine (IBMP).
The problem begins when fungal spores find their way into drinking water systems, often surviving water treatment processes and flourishing within water distribution systems. These fungi can produce compounds that lead to earthy or musty odors, which are detected by consumers even at very low concentrations1. 2-MIB and geosmin are well-known for producing these unpleasant odors and have been found in drinking water at concentrations ranging from 10–256 nanograms per liter (ng/L)—levels that are easily detectable by the human nose.
Odor production: a quick and persistent problem
The study found that fungal odor activity peaked within four days of incubation, meaning that the highest levels of odorants were produced in a very short time. While these compounds reached concentrations detectable by consumers within this timeframe, the toxicity of the fungal contamination continued to increase over eight days. This extended period of toxic buildup poses additional risks, particularly for immunocompromised individuals. Fungi not only cause aesthetic problems in drinking water, but their presence may also signal underlying microbial contamination that could affect water safety2.
While the focus of this study was on aesthetic issues like taste and odor, the persistence of fungal contamination suggests that water treatment facilities need to consider fungi more seriously. Left unchecked, these microorganisms can proliferate rapidly and contribute to long-term water quality degradation3.
The role of UV treatment in reducing fungal contamination
Given the resistance of fungal spores to traditional water treatment methods like chlorination, alternative disinfection strategies are needed. The study emphasized that UV treatment can effectively reduce fungal contamination in drinking water. UV light, a form of advanced disinfection process (ADP), was shown to significantly reduce the abundance of fungal species such as Aspergillus, Fusarium, Rhizopus, and Trichoderma in water systems.
Specifically, the study found that UV treatment reduced the gene read counts of these fungi by 2.3 to 4 times. This reduction suggests that UV light is highly effective at deactivating fungal spores, which are known for their resistance to chlorine disinfection. UV treatment works by damaging the DNA of microorganisms, preventing them from reproducing and thereby mitigating the risk of contamination. The effectiveness of UV disinfection makes it a promising strategy for reducing not only fungal contamination but also the associated taste and odor issues in drinking water.
Health and safety risks
While fungi in drinking water are often considered an aesthetic issue, their presence can pose serious health risks, particularly for vulnerable populations. Immunocompromised individuals are at a higher risk of infection from waterborne fungi, as these organisms can behave as opportunistic pathogens. Fungal spores are particularly resistant to chlorine-based disinfection methods, making them more likely to survive and proliferate in water distribution systems.
In addition to the potential for fungal infections, some fungi can produce mycotoxins—harmful compounds that can be toxic to humans. Although mycotoxin production in drinking water systems has not been extensively studied, the growing recognition of fungi as contributors to taste and odor issues suggests that more research is needed to fully understand the health implications of long-term fungal exposure through drinking water.
Addressing fungal contamination in drinking water in the future
The findings of the Environmental Science & Technology study highlight the previously underappreciated role of fungi in contributing to taste and odor problems in drinking water. While the aesthetic impact of musty or earthy smells may seem like a minor inconvenience, the persistence and resistance of fungi to traditional water treatment methods pose a greater challenge to water quality and public health. UV treatment has emerged as a promising solution for reducing fungal contamination, but more research is needed to understand the full scope of health risks associated with fungi in drinking water.
As we continue to refine water treatment processes, the importance of addressing fungal contamination will likely grow. Future research could explore the potential for mycotoxin production in water systems and develop more effective strategies for preventing fungal contamination. Ensuring that drinking water is both safe and pleasant to drink requires a more comprehensive approach—one that accounts for the complex microbial communities, including fungi, that can impact water quality.
In the meantime, consumers should be aware that unusual tastes or odors in their drinking water may be more than just an annoyance—they could be a sign of fungal contamination that warrants further investigation and mitigation.
References
- Zhao, Heng, Tian Zhang, Hong Wang, Chen Hu, Yu Tang, and Bin Xu. “Occurrence of Fungal Spores in Drinking Water: A Review of Pathogenicity, Odor, Chlorine Resistance and Control Strategies.” Science of The Total Environment 853, (2022): 158626. https://doi.org/10.1016/j.scitotenv.2022.158626. ↩︎
- Wan, Qiqi, Gang Wen, Yuhong Cui, Ruihua Cao, Xiangqian Xu, Gehui Wu, Jingyi Wang, and Tinglin Huang. “Occurrence and Control of Fungi in Water: New Challenges in Biological Risk and Safety Assurance.” Science of The Total Environment 860, (2023): 160536. https://doi.org/10.1016/j.scitotenv.2022.160536. ↩︎
- Zhao, Heng-Xuan, et al. “Overlooked Role of Fungi in Drinking Water Taste and Odor Issues.” Environmental Science & Technology, 5 Sept. 2024, https://doi.org/10.1021/acs.est.4c02575. ↩︎
