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Taste and Odour

The Guidelines for Canadian Drinking Water Quality 1989 states that drinking water should be inoffensive with respect to both taste and odour. Although taste and odour are not regulated as parameters of health concern, they are perhaps the most important characteristics of drinking water from the point of view of perception. It is next to impossible to convince the public that water is safe to drink if it either tastes or smells bad.
Taste and odour continue to be one of the most difficult issues faced by the water treatment industry. They are a problem, at least intermittently, in most surface water supplies and also in a number of groundwater supplies.
Taste and odour problems may be caused by natural organic matter present in the water, by synthetic chemicals or by some inorganic substances. Some compounds in the first two classes may react with disinfectants such as chlorine to produce tastes and odours that are worse than those in the raw water.

Sources

Taste-causing substances in drinking water are generally inorganic compounds while organic constituents of water are the ones that cause odour problems most frequently -either in themselves or through reaction with disinfectants or oxidation processes.

• Biological Sources

Historically, taste and odour problems in the water treatment industry were associated with algae and decaying vegetation. In addition a class of bacteria known as actinomycetes were linked to taste and odour. The identification of earthy-smelling and musty-smelling compounds were isolated from certain actinomycetes cultures. Many types of algae are common in water supplies and are known as causes of tastes and odours. Both living and dead algae can be responsible for tastes and odours. Although not as common, other bacteria, fungi, zooplankton, nematodes and some amoebae are sometimes responsible for taste and odour.

• Man-Made Sources

Tastes and odours attributed to anthropogenic (man-made) sources can include non-point inputs and municipal and industrial wastewater effluents. Non-point sources may come from direct runoff or from upstream stormwater discharges. This problem can be severe in times of high flow after a prolonged dry or frozen spell, typically in springtime.

• During Treatment

Tastes and odours created during treatment can be caused by either biological activity or the addition of treatment chemicals. The oxidants used in water treatment can remove or reduce tastes and odours but under certain conditions can also cause them.

• In Distribution Systems

There are four sources of tastes and odours in distribution systems:

1. Compounds of biological origin
   Tastes and odours of biological origin can be linked to an increase in the number of microorganisms at certain points in the system.
2. Disinfectant residuals and oxidation by-products
   Tastes and odours caused by disinfectant residual can be from the residual itself or the reaction on the organic compound.
3. Emissions from pipes and storage facilities
   In high concentrations, metals such as lead, copper, zinc and iron can cause tastes on the water as a result of corrosion of the plumbing system.
4. Diffusion of pollutants through synthetic pipes
   Some pollutants such as hydrocarbons and phenols may diffuse through plastic piping so care should be given to which way pipes are laid.

• In Household Plumbing

Tastes and odours can be created within ordinary household plumbing. Some examples are metals in high concentrations due to corrosion; hydrogen sulphide forming in hot water tanks; musty odours from inactivity; and odour causing bacteria within certain treatment devices.

Classification and Treatment

It is important to be able to classify an odour that may be detected in drinking water. Classification simplifies odour description, provides a unified terminology, suggests possible sources of odours and may help in choosing the best method of treatment. A taste classification is also required.
The more common descriptors of drinking water odours have been placed in groups. Some of those groups are as follows:

Group 1 - Earthy/musty/mouldy
• Most frequently observed;
• May be detected only after addition of chlorine;
• Can be produced by actinomycetes;
• Very low concentrations can lead to complaints.

Group 2 - Chlorinous
• High frequency of complaints resulting from chlorination.

Group 3 - Grass/hay/straw/wood
• Often associated with algal by-products and sometimes described as decayed vegetation.

Group 4 - Marshy/swampy/septic/sewage/sulphurous
• Very offensive;
• May be of natural or anthropogenic origin (sulphur containing compounds).

Treatment

Aeration, filtration, coagulation, oxidation (disinfection), adsorption, and biological treatment are some of the various treatment methods available in assisting in the removal of tastes and odours from the drinking water.
Some of these techniques may be impractical to some situations and can be costly. If oxidation of the water by disinfection and filtering of the water by granular activated carbon (GAC) is not effective in the removal of the tastes and odours, then an alternate source of drinking water should be obtained.
This usually requires construction/ reconstruction of a water well. This frequently involves the installation of additional casing beyond the length (depth) normally required by regulations.

Contact

Charlottetown

Jones Building

Robison, Alan (Senior Drinking Water Technologist)