Water utilities and laboratory studies have indicated that chlorine or chloramines can mask earthy or musty odours. However, there have been conflicting results. Sensory testing was completed on finished waters from five water utilities and a control to determine whether earthy and musty odours, caused by geosmin and 2-methyl isoborneol (MIB), at concentrations found in drinking water, are dependent on the background water matrix or chlorine (<1 mg l−1 as Cl) or chloramines (2–4 mg l−1 as Cl) concentrations found in finished drinking waters. Finished and dechlorinated water samples were spiked with geosmin and MIB and analysed by Flavor Profile Analysis to determine odour intensity and solid phase microextraction/GC-MS to determine actual geosmin and MIB concentrations. The participating utilities for this project represent a wide range of background matrices in terms of both total organic carbon and total dissolved solids. Background water quality did not significantly affect the intensity of earthy and musty odours. Dechlorination and dechloramination increased the intensity of the earthy odour of geosmin (20.1–61.9 ng l−1). However, dechlorination and dechloramination did not significantly affect the musty odour of MIB (18.6 ng l−1). This may be due to the statistical power of the method used at the low MIB concentration.

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