2,6-dichlorophenol
“Chlorophenol , like antiseptic mouthwash”
2,6-dichlorophenol
170 ng
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
170 ng Threshold
55 ng / l in water Origins
Produced through reactions involving phenolic compounds (for example from waters associated with peaty soils) and free chlorine. Can also arise due to contamination of water with wood preservatives. Importance
Disinfection by-product. Imparts an unpleasant ‘tainted’ note. Described by consumers as ‘medicinal’ or ‘contaminated’, even at low levels. CAS registry number
87-65-0 Other names
1-hydroxy-2,6-dichlorobenzene
2,6-DCP
2,6-dichlorfenol
Remarks
Water pH is important in determining the rate of formation. Can occasionally be produced by bacterial action or by misuse of carbon filters. Threshold distribution
dimethyl disulphide
“Rotten vegetable , like a sewage treatment plant”
dimethyl disulphide
360 µg
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
360 µg Threshold
120 µg / l in water Origins
Formed through biochemical decay of grass and vegetation in reservoirs and lakes, or by metabolism of bacteria or moulds. Importance
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. CAS registry number
624-92-0 Other names
DMDS
dimethyl disulfide
dimethyl disulfane
2,3-dithiabutane
methyl disulfide
(methyl dithio) methane
methyl dithiomethane
methyldithiomethane
methyldisulfanylmethane
Remarks
Often found in association with other sulphur compounds and / or methoxypyrazines. Threshold distribution
dimethyl trisulphide
“Onion , like stagnant water or decaying vegetation”
dimethyl trisulphide
330 ng
Technical specification
Assessment
Cover the sample with your hand and swirl the glass to release the aroma. Remove your hand and take a single long sniff. Repeat as necessary. Amount of flavour per capsule
330 ng Threshold
110 ng / l in water Origins
Formed through decay of grass and vegetation in reservoirs and lakes and by bacterial action. Can also arise from decomposition of algae following an episode of algal bloom. Importance
Imparts an unpleasant ‘swampy’ odour to water. The intensity of the odour can be increased by the presence of other sulphur compounds. CAS registry number
3658-80-8 Other names
DMTS
1,3-dimethyl trisulfane
methyl trisulfide
methyl trithiomethane
methylsulfanyldisulfanylmethane
methyltrithiomethane
2,3,4-trithiapentane
methylsulfanyldisulfanylmethane
Remarks
Often found in association with other sulphur compounds such as H2 S and methanethiol. Threshold distribution
ferrous sulphate
“Metallic , like ink or blood”
Technical specification
Assessment
Take a little sample into your mouth. Move it around with your tongue for a few seconds then swallow it. To confirm, rub a little onto the back of your hand and check for metallic odour. Amount of flavour per capsule
2.7 mg Threshold
900 µg / l in water Origins
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. Importance
Imparts a metallic mouthfeel. High levels may be associated with discolouration of the water supply and – in the extreme – the formation of ‘red water’. CAS registry number
7782-63-0 Other names
ferrous sulfate
iron(2+) sulfate
iron(2+) sulphate
ferrous sulphate heptahydrate
ferrous sulfate heptahydrate
iron(2+) sulfate heptahydrate
iron(II) sulfate heptahydrate
iron(II) sulphate heptahydrate
Remarks
Copper, manganese and other metals can also be responsible for metallic notes in water. Occasionally, lipid oxidation products can give rise to ‘non-metallic’ metallic odours. Threshold distribution
geosmin
“Geosmin , like sugar beets or damp soil”
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
35 ng Threshold
10 ng / l in water Origins
Formed by Actinobacteria, Cyanobacteria and algae in lakes, reservoirs and water distribution systems. Produced by both actively-growing organisms and through cell lysis and decomposition. Importance
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. CAS registry number
23333-91-7 Other names
2beta,6alpha-dimethyl bicyclo(4.4.0)decan-1beta-ol
octahydro-4,8a-dimethyl-4a(2H)-naphthol
2b,6a-dimethyl bicyclo[4.4.0]decan-1b-ol
2beta,6alpha-dimethyl bicyclo[4.4.0]decan-1beta-ol
1,10-(E)-dimethyl-(E)-(9)-decalol
(E)-1,10-dimethyl-(E)-decalin-9-ol
2b,6a-dimethyl bicyclo(4.4.0)decan-1b-ol
2,6-dimethyl bicyclo(6.4.4.06)decan-1-ol
4,8a-dimethyl decalin-4a-ol
4,8a-dimethyl-1,2,3,4,5,6,7,8-octahydronaphthalen-4a-ol
octahydro-4,8a-dimethyl-4a(2H)-naphthalenol
octahydrodimethyl-4alpha-naphthol
Remarks
Most common in surface abstracted waters. Formation can be influenced by weather conditions leading to concentration of organic materials in the water and growth of microorganisms. Threshold distribution
hydrogen sulphide
“H2 S , like boiled or rotten eggs”
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
18 µg Threshold
4 µg / l in water Origins
Formed by anaerobic sulphate-reducing bacteria from sulphate, by Clostridium or Bacillus from sulphite or proteins, or by electrochemical action through corrosion of pipes in systems with very low flow rates. Importance
Imparts an unpleasant sulphury note to water. H2 S is easily oxidized to less odour-active species, so its presence is indicative of the failure of water treatment processes or post-treatment contamination. CAS registry number
7783-06-4 Other names
H2 S
hydrogen sulfide
dihydrogen monosulfide
dihydrogen monosulphide
hydrogen sulfuric acid
hydrogen sulphuric acid
sulfur hydride
Remarks
Often found in association with other sulphur compounds such as methanethiol and dimethyl trisulphide. Be careful not to overexpose yourself to samples with H2 S. The more you look for it the less likely you are to find it. Threshold distribution
2-isobutyl-3-methoxypyrazine
“Earthy , like green pepper”
2-isobutyl-3-methoxypyrazine
30 ng
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
30 ng Threshold
10 ng / l in water Origins
Formed by Actinobacteria in lakes, reservoirs and water distribution systems. May occur in admixture with other methoxypyrazines. Importance
Potent off-flavour with a very low flavour threshold. Imparts an unpleasant earthy note to water which is reminiscent of green peppers. CAS registry number
24683-00-9 Other names
2-methoxy-3-(2-methylpropyl)pyrazine
isobutyl methoxypyrazine
3-isobutyl-2-methoxypyrazine
galbanum pyrazine
2- methoxy-3-(2-methyl propyl) pyrazine
2-methoxy-3-(2-methylpropyl)pyrazine
2-methoxy-3-isobutyl pyrazine
2-2-methyl propyl-3-methoxypyrazine
Remarks
Usually associated with surface water abstraction. Formation can be influenced by weather conditions leading to concentration of organic materials in the water and growth of microorganisms. Threshold distribution
2-methylisoborneol
“Earthy , mouldy, like peat or compost”
2-methylisoborneol
260 ng
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
260 ng Threshold
85 ng / l in water Origins
Formed by Actinobacteria, Cyanobacteria and algae in lakes, reservoirs and water distribution systems. Produced both by actively-growing organisms and through cell lysis and decomposition. Importance
Imparts an unpleasant earthy odour to water which is reminiscent of peat or rotting compost. Extremely odour-active and for that reason one of the most common flavour faults in potable water. CAS registry number
2371-42-8 Other names
1,6,7,7-tetramethylbicyclo[2.2.1]heptan-6-ol
MIB
exo-1,2,7,7- tetramethyl bicyclo(2.2.1)heptan-2-ol
Remarks
Most common in surface abstracted waters. Formation can be influenced by weather conditions leading to concentration of organic materials in the water and growth of microorganisms. Threshold distribution
skatole
“Skatole , like animal faeces”
Technical specification
Assessment
Cover the sample with your hand and swirl the glass to release the aroma. Remove your hand and take a single long sniff. Repeat as necessary. Amount of flavour per capsule
2.0 µg Threshold
700 ng / l in water Origins
Formed by bacteria growing in water, or contributed, pre-formed, by ground water pollution, being produced by bacteria from tryptophan. Importance
In addition to contributing an unpleasant, somewhat nauseating, faecal note to water, the presence of skatole can also indicate contamination of the water supply chain with faecal bacteria. CAS registry number
83-34-1 Other names
beta-methyl indole
β-methylindole
scatole
skatol
3-methylindole
3-MI
3-methyl-1H-indole
3-methyl-4,5-benzopyrrole
Remarks
Indole and DMS may often be found in water which contains skatole. Threshold distribution
2,4,6-tribromoanisole
“Musty , like corked wine with a rubbery overtone”
2,4,6-tribromoanisole
230 ng
Technical specification
Assessment
Without covering the glass, swirl the sample to release the aroma. Take a single short sniff. Repeat as necessary. Amount of flavour per capsule
230 ng Threshold
<10 ng / l in water Origins
Derived from methylation of bromophenols by moulds or Actinobacteria, primarily in water distribution systems. Importance
Imparts an unpleasant musty odour to water which is reminiscent of damp cellars or corked wine. CAS registry number
607-99-8 Other names
tribromoanisole
TBA
1,3,5-tribromo-2-methoxybenzene
methyl 2,4,6-tribromophenyl ether
Remarks
2,4,6-Tribromoanisole is one of several bromoanisoles that can taint water. The flavour produced by this compound is typical. This compound can be detected, but not recognized at concentrations well below the recognition flavour threshold. Threshold distribution
