The importance and origins of each flavour are:

Flavour: CHLOROPHENOL    Chemical name: 2,6-DICHLOROPHENOL

“Chlorophenol, like antiseptic, disinfectant or mouthwash”

IMPORTANCE: Chlorophenols are disinfection by-products. They impart unpleasant ‘tainted’ notes to water. Waters containing chlorophenols are ddescribed by consumers as ‘medicinal’ or ‘contaminated’, even at low levels.

ORIGINS: Chlorophenols are produced in water through reactions involving phenolic compounds (for example from waters associated with peaty soils) and free chlorine. They can also arise through to contamination of water with wood preservatives.

Flavour: ROTTEN VEGETABLE    Chemical name: DIMETHYL DISULPHIDE

“Rotten vegetable, like pickled vegetables or a sewage treatment plant”

IMPORTANCE: Dimethyl disulphide Imparts an unpleasant reduced sulphur note, reminiscent of decaying vegetation. The intensity of the odour can be increased by the presence of other sulphur compounds.

ORIGINS: Dimethyl disulphide (DMDS) is formed through biochemical decay of grass and vegetation in reservoirs and lakes, or by metabolism of bacteria or moulds.

Flavour: METALLIC    Chemical name: FERROUS SULPHATE

“Metallic, like ink or blood”

IMPORTANCE: Ferrous ions Impart a metallic mouthfeel to water. High levels of ferrous ions may be associated with discolouration of the water supply and – in the extreme – the formation of ‘red water’. Addition of one capsule of this flavour standard to one litre of water produces a colourless solution, whereas use of two capsules in one litre of water produces a discoloured solution.

ORIGINS: Metallic taints are derived from contamination of water with metal ions, either from natural ground and soil conditions or from electrochemical or microbe-mediated corrosion of cast iron pipework.

Flavour: GEOSMIN    Chemical name: GEOSMIN

“Geosmin, like sugar beets or damp soil”

IMPORTANCE: Geosmin imparts an unpleasant earthy odour to water which is reminiscent of sugar beets or damp soil. Extremely odour-active and for that reason one of the most common flavour faults in potable water.

ORIGINS: Geosmin is formed in water by Actinobacteria, Cyanobacteria and algae. These can be found in lakes, reservoirs and water distribution systems. Geosmin is produced by both actively-growing organisms and through cell lysis and decomposition.

Flavour: EARTHY-GREEN PEPPER    Chemical name: 2-ISOBUTYL-3-METHOXYPYRAZINE

“Earthy-green pepper, like green pepper or chillies”

IMPORTANCE: 2-Isobutyl-3-methoxypyrazine is a potent off-flavour with a very low flavour threshold. It imparts an unpleasant earthy note to water which is reminiscent of green peppers.

ORIGINS: 2-Isobutyl-3-methoxypyrazine is formed by Actinobacteria in lakes, reservoirs and water distribution systems. It may occur in admixture with other methoxypyrazines.

Flavour: EARTHY-POTATO SKINS    Chemical name: 2-ISOPROPYL-3-METHOXYPYRAZINE

“Earthy-potato skins, like potato skins or dug soil”

IMPORTANCE: 2-Isopropyl-3-methoxypyrazine imparts a potent off-flavour with a very low flavour threshold. It gives an unpleasant mouldy / musty note to water which is reminiscent of potato skins or dug soil.

ORIGINS: 2-Isopropyl-3-methoxypyrazine is formed by Actinobacteria in lakes, reservoirs and water distribution systems. It may occur in water in admixture with other methoxypyrazines.

Flavour: RANCID OIL    Chemical name: TRANS,TRANS-2,4-HEPTADIENAL

“Rancid oil, like potato chips or vegetable oil”

IMPORTANCE: 2,4-Heptadienal Imparts a rancid oil note to water, reminiscent of cod liver oil. At higher concentrations the odour of heptadienal can be perceived as fishy.

ORIGINS: 2,4-Heptadienal is formed by algae in lakes and reservoirs. It is produced by both actively-growing organisms and through cell lysis and decomposition.

Flavour: EARTHY-COMPOST    Chemical name: 2-METHYLISOBORNEOL

“Earthy-compost, like compost or peat, mouldy”

IMPORTANCE: Methylisoborneol imparts an unpleasant earthy odour to water which is reminiscent of peat or rotting compost. It is extremely odour-active and for that reason is one of the most common flavour faults in potable water.

ORIGINS: Methylisoborneol (2-MIB) is formed by Actinobacteria, Cyanobacteria and algae in lakes, reservoirs and water distribution systems. It is produced both by actively-growing organisms and through cell lysis and decomposition.

Flavour: CUCUMBER    Chemical name: TRANS,CIS-2,6-NONADIENAL

“Cucumber, like cucumber skin or watermelon”

IMPORTANCE: Nonadienal imparts a pleasant, but nevertheless atypical, cucumber-like note to water, which is reminiscent of water melon at high concentrations.

ORIGINS: Nonadienal is formed by algae in lakes and reservoirs. It is produced both by actively-growing organisms and as a result of cell lysis and decomposition. Cucumber-like odours from nonadienal can also be formed in water from amino acids as a by-product of ozonation.

Flavour: MUSTY-TCA    Chemical name: 2,4,6-TRIBROMOANISOLE

“Musty-TBA, like corked wine or a damp cellar”

IMPORTANCE: 2,4,6-Tribromoanisole imparts an unpleasant musty odour to water which is reminiscent of damp cellars or corked wine.

ORIGINS: 2,4,6-Tribromoanisole is derived from methylation of bromophenols by moulds or Actinobacteria, primarily in water distribution systems.