The most common use of the absorption process in commercial water treatment is the reduction and removal of taste- and odor-causing substances in water. Certain compounds and organisms in water, while they have no bearing on the hygienic safety of water supplies, are nevertheless, offensive to either taste or smell–or both. some persons have greater sensitivity t smells and taste than others. Basically, there are four categories for taste: bitter, sweet, sour, and saline. Since human taste buds and olfactory organs generally function in unison, it is difficult to separate the two. One way to distinguish taste from odor is by holding the nose and swallowing a sample of water. Out-of-town visitors often recognize off-tasting water that local residents have long been accustomed to and no longer notice.

Numerous labels have been given to odors in water, among the 20 or so identified ones are cucumber, earthy, fishy, grassy, and sulfur. The cucumber flavor in drinking water has been identified as trans, 2-cis, 6-nonadienal produced by an algae growth beneath the ice in the Cannonsville Reservoir, which supplies the Baxter Plant of the city of Philadelphia, Pa. In the absence of any official quantitative measurement of taste and odors, it is quite common to have a panel of several persons in a laboratory determine the presence or absence of taste and odor in a given product, including water supplies. One erroneous comment often quoted is that “hydrogen sulfide gives water an awfully bad taste,” whereas, in reality, it is the hydrogen sulfide (H2S) gas odor (rotten egg) that is being detected. It is said that the human nose is 100 times as sensitive in detecting threshold odor values as the best analytical apparatus available today.

Undesirable taste/odor characteristics in water supplies emanate from several sources. First are the results of chemical disinfection. Second, are those arising from the presence of certain organisms (nonpathogenic) usually found in such water supplies as rivers and lakes. Third are those due to man-made conditions, such as chemicals, solvents, and pesticides will impart a distinctive odor to water supplies, several others have n telltale taste or odor, so their presence in drinking water can be more subtle. A fourth category includes odors associated with dissolved gases, such as the “sulfur odor” where hydrogen sulfide exists.