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A search for the cause of Edmonton's spring time taste and odour events occurring in two successive years implicated four low molecular weight aldehydes: 2-methyl propanal, 2-methyl butanal, 3-methyl butanal and phenylacetaldehyde. Food science literature reports threshold odour values at µ.g/l levels for these chemicals. Observations of a more intense odour in treated than in raw water suggested the possibility of these compounds being produced in the treatment process. The chemistry literature suggests the likelihood that these chemicals could arise as oxidation products of corresponding amino acids. This expectation has been experimentally confirmed for chlorination and chloramination of water supplies.

This article reviews the use of the Ames Salmonella assay for assessing the mutagenicity of water produced by various treatment processes. Although chlorination is the most common means of disinfection in North America, chloramines, chlorine dioxide, and ozone have been shown to produce water that is less mutagenically active. Granular activated carbon (GAC) removes mutagens preferentially compared with parameters such as total organic carbon. In the absence of GAC, postchlorination typically increases mutagenicity. Inconsistent interstudy results with respect to the effects of ozone and metabolic activation (S9) and the capacity of GAC point to the role of raw water characteristics in the determination of treated water mutagenicity. In the case of ozone, dosage and contact time may also be important.