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Drinking Water - Taste and Odour
Where can I find information on Drinking Water Standards?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.
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 actinomyceteswere 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.
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.
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.
There are four sources of tastes and odours in distribution systems:
- 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.
- 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.
- 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.
- 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.
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.
Classifications
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 listed below:
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.
Charlottetown
Jones Building
Robison, Alan (Senior Drinking Water Technologist)