Get Informed | Color, Taste, and Odor (Smell)

What are Color, Taste, and Odor? 

The EPA drinking water standards include a group of standards that are known as the secondary drinking water standards. These standards or guidelines are not regulated by the federal, but by state government. The secondary drinking water standards were set for aesthetic and technical reasons and not for specific health standards. In addition, there are specific standards that relate to the color, odor (threshold odor number), and Turbidity of the water. Even though the taste of the water is not regulated, the taste of the water can also indicate a potential problem with your water.

How does Color, Taste, or Odor become a problem? 

The color, taste, and odor of the water are related to various contaminants or conditions of the water that create a nuisance, adversely impact the general use of the water, or create an aesthetic issue that does not encourage the user to drink, use, or bathe/shower in the water. Even though these conditions may only be a nuisance, they may also suggest that a contaminant may be present that can create a health problem.

What are the Health Risks for Color, Taste, or Odor?

Just because the water has a color, taste, or odor, this does not mean that the water is toxic, a health risk, or unsafe to drink; it means there is a nuisance. In some cases, the color, taste, and odor can suggest the presence of something else that is a health concern.

Color – If the water has a bluish-green or green color this could suggest the water is corrosive and may contain elevated levels of copper, lead, zinc, or other trace metals. If the water has a grayish tint the water may contain elevated levels of Aluminum and blackish water could suggest the presence of elevated levels of Copper, Iron, and Manganese sulfides or oxides and sulfate-related/iron or manganese Nuisance Bacteria. If the water looks like tea, this may suggest the presence of elevated levels of tannic and fulvic acids, partially decomposed organic material, or potentially elevated levels of Iron.

Taste – If the water has a metallic taste, the water may be Corrosive and/or contain elevated levels of metals, such as: Iron, Manganese, Copper, Lead, Zinc and other metals.

Odor (Smell) – Phenolic/Strong smell – petrochemicals and volatile organics; Chemical Smell – synthetic organic compounds and industrial chemicals; “methane”- like smell – mercaptans ; Oily Smell – gasoline/petrochemicals/surfactants; Rotten Egg Smell – Sulfur, Hydrogen Sulfide, microbiological contaminants; Perfume Smell – surfactants; Fishy Smell – surfactants, barium, cadmium, high organic matter, algal blooms in surface water sources, or reaction with chloramine/ammonia in water; Musty / Earthy Smell – Iron  Bacteria, mold, fungi, algal blooms in surface water sources, or high bacterial count; Cucumber Smell – may be related to algal blooms and Iron  Bacteria; Chlorine Smell – high levels of chlorine and chlorine by-products.

What are the Standards for Color, Taste, and Odor?

The secondary drinking water standards are as follows:

Color – 15 color units Odor – Threshold

Taste – Foaming Agents – Foaming is usually caused by detergents and similar substances when water has been agitated or aerated as in many faucets. An off-taste, described as oily, fishy, or perfume-like, is commonly associated with foaming, cloudy, and bitter taste. However, these tastes and odors may be due to the breakdown of waste products rather than the detergents themselves. Standard – 0.05 mg/L.

Odor – Number (TON) of 3

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Threshold Odor Number (TON) | How is it Determined?

Sample Volume
Diluted to 200 mL
Threshold Odor
Number (TON)
Sample Volume
Diluted to 200 mL
Threshold Odor
Number (TON)

200
1
8.3
24

100
2
5.7
35

70
3
4
50

50
4
2.8
70

35
6
2
100

25
8
1.4
140

17
12
1
200

Source: Civil Engineering Department of Virginia Tech.

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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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Aluminum – 0.05 to 0.2 mg/L; characterized by discolored water (gray, grayish white)

Copper – 1 mg/L; metallic taste, blue-green staining

Corrosivity – should be non-corrosive to avoid corrosion, elevated levels of metals, metallic taste.

Iron – 0.3 mg/L; rusty, discolored water, and staining, sediment, metallic taste.

Manganese – 0.05 mg/L; black to brown water, black staining, bitter metallic taste.

Silver – 0.1 mg/L; gray skin discoloration and graying of the eye.

Sulfate – 250 mg/L; salty taste and laxative effect.

Total Dissolved Solids – 500 mg/L; salty taste, corrosion, scale formation (high hardness), scale-forming water.

Zinc – 5 mg/L, metallic taste.