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Physical and biological parameters that affect taste and odor of water

Water supplying agencies must insure consumers are provided with palatable water, as well as safe water, at all times. The water must be free of any detectable taste and odor. Taste is determined in the drinking water by sensory methods which are then expressed as salty, brackish, fresh, bitter, acidic, metallic, soapy, hard or earthy. Odor is also identified by sensation and can be expressed as putrefactive, musty, fishy, phenolic, chlorine, etc. Taste and odor occurrences may develop unaccompanied or as a combination of both due to same conditions and sources. Presence of taste and odor in a water sample may be attributed to following physical and biological characteristics.

Physical Characteristics
Color and turbidity in water is suggested to be due to presence of colloidal particles in high concentration in the water and can be known by assessing the clarity of water. However detection of taste and odor can be very problematic.
- pH
pH influence taste and odor of water in instances where it controls the equilibrium concentration of neutral and ionized forms of a substance in solution. Reactions that produce products with intense flavors are also influenced by pH, such as chlorophenols.
- Chlorine
Chlorine is the most widely used in water for disinfection purposes. Acording to Water quality criteria (1963) objectionable tastes and odors may be produced by residual chlorine concentrations but above 2.0 mg/L. Although free chlorine residuals do produce tastes and odors, the objectionable situations are usually attributed to presence of chlorinous compounds. Some chloro-derivatives which form during the treatment process may be more undesirable as taste and odor, such as bitter to medicinal, chlorination odor and pungent chlorinous odors.
- TDS
Total dissolved solids (TDS) has strong relation with the taste of water. Following are the grades of potability by total dissolved solids (TDS) levels, developed during a study in California.
Water Portably Scale with respect to concentration Of TDS: excellent;less than 300 mg/L, good;301-600 mg/L, fair;601-900 mg/L, poor;901-1200 mg/L
- Mineral Cations
Following taste thresholds values are assigned for the major cations of drinking water that are calcium, magnesium, sodium and potassium to be approximately 125 mg/L, 100 mg/L, 30-140 mg/L and 340-680 mg/L, respectively. Small quantities of iron adversely affect the taste of water i.e. 0.04 mg/L in distilled water and 0.12 mg/L in mineralized spring water.
- Fluoride
Fluoride at a concentration of 1 mg/L may impart an undesirable taste to water. sodium fluoride at a concentration as low as 2.4 mg/1 fluoride can bring a salty taste in water.
- Sulfur
Sulfate compounds cause pungent odor and taste in drinking water. It can also support the growth of sulfate reducing bacteria which converts the sulfate ions to hydrogen sulfide. The hydrogen sulfide gas, which is produced, causes a foul, rotten egg odor.

Microbiological Characteristics
The odors caused by dead organic matter are usually vegetable odors and odors of decomposition. The decaying vegetation, such as algae, grass, leaves, and underwater weeds, usually result in an odor which may be characterized as grassy or musty. The production of low concentrations of metabolic products by certain organisms in water can result in offensive tastes and odors. Bacterial activity in relation to mineral matter is also the chief causes of tastes and odors in contaminated water.

References:
(2009,10). Welcome to the Health Canada Web site | Bienvenue au site Web de Santé Canada. Taste [Technical document - Chemical/Physical Parameters]. Retrieved October, 2014, from http://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/taste-gout/index-eng.php#...
McKee, J.E. and Wolf, H.W. (eds.). (1963). Water quality criteria. 2nd edition. Publ. No. 3-A, State Water Quality Control Board, Sacramento, CA
Tölgyessy, J. (1993). Google Books. Chemistry and Biology of Water, Air and Soil: Environmental Aspects - Google Books. Retrieved October, 2014, from http://books.google.com.pk/books?id=Xl2IPX22TEAC&dq=Water+quality+and+tr...(1971)&source=gbs_navlinks_s
Lin , S.D. (1997). Illinois State Water Survey - Home, University of Illinois at Urbana-Champaign. Tastes and Odors in Water Supplies — A Review . Retrieved October, 2014, from http://webh2o.sws.uiuc.edu/pubdoc/C/ISWSC-127.pdf