Odour and Taste:

The dissolved organic materials, inorganic salts and dissolved gases impart taste and odour to water. Although taste and odour occur together, there are certain non-volatile substances such as sodium chloride, which give rise to tastes without causing odour. For drinking purpose, water must not contain any undesirable or objectionable taste and odour. However, taste imparted by dissolved oxygen and dissolved carbon dioxide are generally desirable.

Taste and odour is a subjective test which may be expressed upon description rather than quantitative results, but many times the extent of taste and odour of a sample is measured quantitatively by threshold odour number or simple threshold odour. The threshold odour number represents the dilution ratio at which the odour is hardly detectable. Water sample to be tested is gradually diluted in the ratio of 1:4 with distilled water. The mixture at which the detection of odour by human observation is lost is determined. The number of times and the sample is diluted are represents the threshold odour number.