THE DETERMINATION OF TASTE AND ODOUR IN DRINKING WATER IN RELATION TO WATER QUALITY REGULATIONS
Report No FR0254
R I Crane
To review the methods of analysis for the assessment of taste and
odour with respect to UK Regulations concerning the quality of
drinking water and to recommend laboratory studies to develop
The assessment of drinking water for odour and taste is one of the
more basic tests carried out by water undertakers and it is one of
the few water quality assessments that consumers can readily carry
out themselves. The Water Supply (Water Quality) Regulations 1989
(and their Scottish equivalents) have set mandatory standards for
odour and taste in drinking water. Such standards for what is a
subjective assessment lead to many methodological and
interpretational problems. The methodology available and associated
problems need to be reviewed in order that more reliable techniques
can be identified and developed.
The taste and odour standards in the EC Directive do not reflect
that the determinations required are very subjective and the results
will have considerable uncertainty attached to them. None of the
currently-used methods are likely to produce results with the UK
target precision of +/-1 dilution number.
The meaning of the numbers specified in the Directive appears to
have been interpreted differently in the UK and some other Member
States. The UK has introduced a scale which appears to be one point
more lenient than used elsewhere. However, any real differences
would probably be masked by the inherent lack of precision of the
Odour and taste are not precisely definable entities and any
numerical value obtained is very dependent on the method used.
Therefore in order to produce results comparable between different
water undertakers a standard method must be used. At present a
variety of methods are used in the UK and Europe and there would
probably be differences in the results produced by these methods. A
CEN task group is attempting to produce a harmonised (standard)
method for the assessment of taste and odour in drinking water. This
CEN method could become the standard method for all in the future in
relation to testing compliance with the EC Drinking Water Directive
and national regulations.
More specific conclusions related to the methodology of taste and
odour compliance testing are given. In addition other conclusions on
the assessment of taste and odour in drinking water are drawn which
are not directly related to compliance with regulations.
- Pressure should be maintained for the revision of the taste and
odour parameters in the EC Directive to provide more sensible and
fully-documented standards. This documentation should include the
purpose of compliance with the standard and the accuracy of
associated analytical methods required to assess compliance.
- The analytical method should be standardised to guarantee
- Any further development and testing of methodology undertaken in
the UK should be compatible with the development of the "standard"
method by CEN.
- Whatever method is used, its performance needs to be determined.
Some further work is needed on determining which are the best
statistical procedures for assessing the performance of the method
and relating this to how compliance with a standard will then be
judged from the results. It may be that the apparently inevitably
low levels of precision of this type of method will override the
apparent justifications for some of the method refinements suggested
- The stability of samples needs to be studied, especially in
relation to odour.
- Some investigation on how any standard methods cope in practice
with a wide range of substances, particularly very volatile
chemicals, is required. The work should involve testing how a range
of substances with differing volatilities achieve equilibrium vapour
concentrations under test conditions.
- The standard method should include a screening process whereby
samples which have virtually no taste or odour can be excluded from
the expensive, full-scale test procedure.
- The panel size should be in the region of eight for full-scale
testing and no more than three for screening. The pool of available
panellists should be large enough to ensure that the same people do
not always form a panel.
- Panels members should be trained and have known sensitivities to a
range of specific substances and also, if possible, to real samples.
The question of whether a panel should consist of "average" or
"sensitive" people still needs to be resolved.
- The performance of panellists should be monitored.
- When presented with a set of samples containing a dilution of the
test sample and reference samples panellists may be required to
identify which sample they regard as not being the reference
("forced-choice" method) or they may be allowed to say that they
cannot tell the difference. The statistical correction required in
the forced-choice method is known but the statistical implications
of the alternative method should be investigated.
- The choice of reference water is an area of uncertainty. The best
option appears to be a groundwater of consistent quality which is
reasonably close to the mineral content of the range of waters to be
tested. A more detailed assessment of how the reference water
affects the result of a test is needed.
- Procedures for running control samples should be included in the
design of a method.
- A room and apparatus should be reserved for taste and odour
- Qualitative testing for taste and odour has a useful role. There
is room for greater standardisation in qualitative testing. There
are some good reasons (sample instability, showing good customer
relations etc) for training samplers to perform this type of
testing. A standard list of descriptors of tastes and odours should
The report outlines the regulations that cover the assessment of
taste and odour in drinking water, discusses the underlying
principles of such assessments and describes the various approaches
used in the UK, Europe and elsewhere. The review is based on
available literature and discussion with laboratories carrying out
such assessments in the UK and Europe.
Copies of the Report are available from FWR, price £35.00 less 20% to FWR Members