Ozone treatment of drinking waters has been applied for a range of purposes including taste and odour control, inactivation of protozoan parasites, degradation of cyanotoxins, ‘enhanced coagulation’, ‘enhanced biodegradation’ and oxidative degradation of recalcitrant organics. Molecular ozone reacts at unsaturated sites of natural organic matter (NOM) to produce smaller oxygenated molecules including carbonyl compounds such as aldehydes, ketones, and carboxylic acids. The elucidation of the nature and precise identity of these ozonation by-products is hindered by two complicating factors. The first is the inherent aqueous solubility of many of these compounds, which renders their efficient extraction from water difficult to achieve. Second is the lack of established identity of specific potential by-products, which complicates targeted analytical approaches. To address these challenges, we have approached the task of by-product identification by methods involving aqueous functional group-specific derivatisation reactions. A range of carbonyl byproducts were identified during laboratory-scale testing. These ranged in size from formaldehyde up to 7-carbon species with multiple carbonyl and hydroxyl functional groups.