Odor and taste of water are closely associated and it is difficult to clearly differentiate between them. Neither parameter assesses the safety of drinking water but both determine its consumer acceptability. Ozone can solve taste and odor problems. Inorganic compounds such as iron, copper, and zinc can be tasted in distilled water at concentrations of 0.05, 2.5, and 5 mg/L respectively. However, only iron is likely to be present at such concentrations in potable water. Hydrogen sulfide may also cause characteristic tastes, often described as smelling like rotten eggs. Both reduced sulfur compounds and iron may be eliminated by oxidation with ozone. In the majority of cases, odors are attributable to organic compounds present in very small concentrations. The organisms responsible for creating taste and odor in water are principally actinomycetes and blue-green algae (cyanobacteria). For example, synura (a species of algae) produces unsaturated aldehydes, which are important odor by products, and are readily oxidizable by ozone.
The effect of ozonation and subsequent treatment on the taste threshold number at the Saint-Maur Pilot Plant (France) can be seen in the table below: