The Hidden Threat: Understanding and Managing Fungi in Water

The recent TV program ‘The Last of Us’ was a sci-fi exploration of a fungal pathogen out-of-control. But should we be concerned about fungal presence in our water supplies?

Water is essential for sanitation and our well-being. However, there's a hidden threat lurking within it: fungi. These microorganisms can thrive in water sources and pose risks to both human health and the environment. Fungi are eukaryotic organisms that consume organic matter to survive. They can exist in a variety of life stages: dormancy, germination, aggregation, and biofilm. This can make their control in water supplies particularly complex to manage.

Fungi are ubiquitous in nature, and water serves as an ideal medium for their growth. Various types of fungi, including mould and yeasts, can be found in lakes, rivers, groundwater, and even tap water. Factors such as temperature, nutrient availability, and pH levels influence their proliferation, making water systems vulnerable to fungal contamination.

While most fungi are harmless, some can pose serious health risks, especially to individuals with weakened immune systems. Globally widespread species such as Aspergillus flavus can produce mycotoxins, which can cause various health problems when ingested in contaminated water. These toxins have been associated with respiratory issues, allergic reactions, skin irritation, and even more severe conditions in individuals with weakened immune systems. In addition, fungal biofilms can incorporate opportunistic and pathogenic organisms and shield them from the residual disinfectant within water supply networks.

Biofilms are complex microbial communities that adhere to surfaces, and they provide a protective environment for fungi, enabling them to survive and reproduce. They can form on a range of surfaces, including pipes, plumbing fixtures, storage tanks, and filters. Once established, biofilms become challenging to remove and can act as reservoirs for fungal growth. This poses a significant risk, as biofilms can release fungal spores into the water, increasing the chances of contamination and proliferation. Fungal growth in water can lead to undesirable changes in taste and odour, rendering it unpalatable and discouraging consumption. The presence of biofilms can obstruct water flow, decrease system efficiency, and contribute to corrosion. These issues can lead to costly repairs and increased maintenance requirements.

Disinfection: A Vital Defence

To combat the growth of fungi and biofilms, disinfection of water supplies becomes crucial. Traditional methods such as chlorination have long been employed to kill or inhibit microbial growth. However, some fungi are more resistant to these disinfectants (CT value reported to be 60 mg·min/L for 80% inactivation of Acremonium, Aspergillus and Penicillium¹), necessitating the development of new strategies. Alternative disinfection methods, such as ultraviolet (UV) light and advanced oxidation processes, are being explored to effectively target fungal species and biofilms.

Effectiveness of treatment processes is often evaluated by using culture-based detection methods to assess the inactivation or removal of micro-organisms. However, these methods rely on micro-organisms to be alive and reacting with the media substrate, and because fungi can exist in a dormant state, they may go un-detected within our water supply networks until a turbidity issue is noticed or taste and odour complaint is raised.

Climate Change: Amplifying the Threat

Climate change is altering environmental conditions worldwide, including temperature and precipitation patterns. These changes can influence the occurrence and distribution of fungi in water, potentially exacerbating the risks they pose². Rising temperatures can promote the growth of fungi, leading to more frequent and severe biofilm formation. Consequently, this could lead to greater challenges in maintaining clean water supplies.

The occurrence and control of fungi in water present a multifaceted challenge that requires attention from both scientists and policymakers. Understanding the role of biofilms, implementing effective disinfection methods, and developing new detection methods are vital steps in mitigating the risks associated with fungal contamination. Furthermore, as climate change continues to unfold, it is crucial to anticipate and adapt to the evolving threats posed by fungi in water. By addressing these issues collectively, we can strive to ensure safe and clean water supplies. While it might not be like an episode from ‘The Last of Us’ quite yet, fungi do make our watchlist for emerging microbial challenges.

1. Pereira, V.J., Marques, R., Marques, M., Benoliel, M.J., Barreto Crespo, M.T., 2013. Free chlorine inactivation of fungi in drinking water sources. Water Research. 47, p.517–523
2. Wan, Q., Wen, G., Cui, Y., Cao, R., Xu, X., Wu, G., Wang, J. and Huang, T., 2023. Occurrence and control of fungi in water: New challenges in biological risk and safety assurance. Science of The Total Environment, 860, p.160536.