Drinking Water Smells, Smelly Water, Taste 
and Odor Problems- Threshold Odor Number (TON)


Besides the parameters described in this report, the color, appearance, taste, smell, and odor of drinking water is the first clue to the homeowner that there may be a problem with the water.

It is important to note that some chemicals, especially organic compounds and bacterial agents, may be at toxic or at pathogenic (i.e., disease causing) levels, without any observable clues to a problem. For this reason, it is recommended that you have your water tested at least annually. Table 1 describes the common water quality problems that may be detectable based on the taste, odor, or appearance.

Primary treatment method used to handle taste, smell, odor, or color problems may include filtration, filtration through a carbon filter, softening, reverse osmosis, chlorination and distillation. The type of pretreatment would depend on the concentration and type of contamination and associated water quality.

Taste, Smell, Odor, and Color and 
Associated Potential Problem

Taste Problems

 Salty-brackish High sodium
Alkali Taste

Oily, Fishy,
or Perfume-Like Tase

High hardness, total dissolved solids, high alkalinity


Metallic Taste Low pH, high metal content, corrosive water

A metallic taste can be caused by inorganic
chemicals such as iron (at levels over 0.004 mg/l), manganese (> 0.1 mg/L) copper (2-5 mg/l), and zinc (4-9 mg/l), nuisance bacteria


Odor / Smell Problems Drinking Water

Rotten-Egg Odor Smell Musty Odors Smell Earthy, musty, grassy, fishy, vegetable and cucumber Hydrogen sulfide, sulfate-reducing bacteria, Softwater reactions in electric water heaters, algal by-products, bacteria, algal by-products, surfactants
Oily Smell Gasoline or oil contamination, possibly nuisance bacteria
Methane Like Gas Smell Organic decomposition - note natural gas has no odor, but the natural gas delivered to your home has mercaptans (sulfur -compounds)
added that create a strong odor to help detect leaks.
Phenolic Smell Industrial or gasoline contamination
Chemical  Smell Organic chemicals, Industrial




Milky Precipitation of carbonates, excessive air, suspended solids
Blackish Tint Reactions with manganese and possibly iron, IRB/ Slime Bacteria, anaerobic bacteria
Yellowish Tint  Presence of humic or fluvic compounds, iron, IRB bacteria, anaerobic/aerobic bacteria
Reddish Tint 

Presence of Dissolved or precipitated iron, iron, IRB bacteria,  anaerobic/aerobic bacteria

Surfactants - Foaming Agents

(Source: Driscoll, 1986; Lehr, 1980; Oram, 1990)

Threshold Odor Numbers- How They Are Determined

Source: Civil Engineering Department of Virginia Tech

TON =  (A + B)/ A
A - Volume of Sample with odor
B - Volume of Pure Water with no odor Added

If A was a 100 ml sample and 100 ml of water had to be added to not detect the odor - the TON would be 2.
TON =  (100 + 100)/ 100

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