Overlooked Role of Fungi in Drinking Water Taste and Odor Issues

Taste and odor (T&O) are among the most frequently encountered aesthetic issues in drinking water. While fungi have been reported to produce offensive odors, their contribution to T&O in drinking water remains understudied and often overlooked. In this study, the profiles of fungal community and odorants produced by 10 native fungal isolates were investigated in 36 samples collected from two drinking water treatment plants and a premise plumbing system. A total of 17 odorants were identified with <i>Penicillium</i>, <i>Aspergillus</i>, <i>Paecilomyces</i>, and <i>Alternaria</i> genera exhibiting the highest odorant yields. Significant concentrations of musty/earthy compounds were produced by these fungal isolates, such as 2-methylisoborneol (2-MIB) (26-256 ng/L), geosmin (10-13 ng/L), and 2-isobutyl-3-methoxy-pyrazine (IBMP) (3-13 ng/L). The high odor activity value of the odorants primarily occurred within 4 d, while toxicity continued to increase during the 8 d incubation. UV treatment in premise plumbing significantly (<i>p</i> < 0.05) reduced the gene read counts of Ascomycota phylum, <i>Aspergillus</i> spp., <i>Fusarium</i> spp., <i>Rhizopus</i> spp., and <i>Trichoderma</i> spp., by 2.3-4.0 times. These findings underscore the previously underestimated role of fungi in contributing to T&O issues in drinking water and corresponding risks to consumers and indicate UV as a promising strategy for fungal control in drinking water.