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Improvements in analytical methods now allow us to measure minute
quantities of chemicals and microorganisms in water which a decade
ago would have been undetectable. However, our understanding of the
impact on public health of low-level exposures to these contaminants
lags far behind the technological expertise which enables us to
detect them. The rationale for testing drinking water needs to be
placed in perspective with the more important aspects of overall
system management and risk minimisation.
Testing of drinking water shares some similarities with laboratory
testing in medicine. Before embarking on a testing regimen, the
reliability of the testing method needs to be established, the
purpose of the test should be clear, and there must be an adequate
response plan to deal with the result. The mere fact that a particular
test exists does not justify its use -- these three requirements must
also be fulfilled.
Some critical factors in drinking water require continuous
monitoring, as even temporary disruption can have major health
consequences. An obvious example is monitoring of chlorine
concentrations to ensure effective destruction of waterborne
pathogens. Failure of chlorination systems is one of the more common
causes of waterborne disease outbreaks.1
Also frequently monitored are levels of faecal coliform bacteria,
which, although not pathogenic, are an early indication of faecal
contamination. Increased levels provide a warning of failure in
water treatment or a break in the integrity of the distribution
system, or possible contamination with pathogens. Tests for faecal
coliform bacteria are cheap, reliable, and rapid. High levels of
faecal coliforms may indicate an elevated risk of waterborne
gastroenteritis.2
Chemical contaminants in drinking water (eg, arsenic or pesticides)
require considerably less frequent measurement, because exposure
to the guideline level does not pose a significant health risk over a
lifetime's consumption. These health guideline levels are very
conservative and have built-in safety factors to compensate for
limitations in scientific knowledge and variation in sensitivity
among the exposed population.3
For all potential waterborne contaminants, including
individual pathogens such as Cryptosporidium and
Giardia, there is a great temptation to attempt to apply
numerical limits. This is understandable: a numerical value is
easily understood and compliance can be clearly judged by regulators
and water authorities alike. However, as illustrated by the at times
frenzied debate accompanying the water contamination episode in
Sydney in 1998, some contaminants can not be equated with a meaningful
health-based guideline value.4
Despite this, the United Kingdom government is pressing ahead with
enforcing a numerical limit for Cryptosporidium in drinking
water and daily monitoring of a large number of water supplies. The
legislation will impose a legally enforceable maximum
concentration of 10 oocysts/100 L for water supplies considered to be
at risk of contamination.5 The presence of
Cryptosporidium oocysts above this level will constitute a
criminal offence, and could result in an unlimited fine. The impetus
for this legislation is complex and relates to an inability under UK
law to prosecute water authorities for outbreaks of waterborne
cryptosporidiosis on the basis of epidemiological evidence.
It is estimated that the cost of testing treated drinking water for
Cryptosporidium in the UK will be at least £8 million per year.
It has been assumed that this improved management of drinking water
treatment plants may prevent about 150 reported cases of waterborne
cryptosporidiosis annually. Thus, the cost of preventing each
reported case would be about £53 000.5 Reported cases probably
represent about one-tenth of community cases,6 making the cost
per community case prevented closer to £5300. These data illustrate
the potentially enormous costs of water testing for individual
pathogens, and the disproportionate cost-benefit relationships
generated when arbitrary limits are imposed without regard for
public health evidence.
Overemphasis on numerical guidelines also leads to compliance
with "the numbers" becoming the primary focus of drinking water
quality management. This simplistic interpretation disregards the
proper and intended role of numerical guidelines as a basis for
verifying the integrity of operational barriers and water treatment
processes. Deviation from normal values may not necessarily
constitute an immediate public health risk, but it signals a need to
identify the cause and, if neccessary, intervene to restore
operational control.
The Australian Drinking Water Guidelines drawn up by the National
Health and Medical Research Council (NHMRC) in 19963 recognise the
primary importance of the multibarrier approach for minimising
health risks in water supply systems, but there has been a recent
tendency for this message to be overlooked by both regulators and
water utilities. The Sydney contamination episode has had
widespread repercussions in the Australian water industry, but one
very positive outcome has been the recognition that a preventive risk
management approach offers a better means of protecting public
health than a reactive response centred around intensified testing
of drinking water.
The current review of the 1996 NHMRC Australian Drinking Water
Guidelines7 will consider expanding the
existing elements of system management and integrating them into a
comprehensive risk-based framework for water quality management,
emphasing prevention rather than reaction. For example, improved
management of agriculture and recreation in catchment areas will
reduce the potential for contamination. This approach includes (i)
systematic assessment of each water system from catchment to tap to
identify hazards and prioritise risks specific to the system; (ii)
establishment and documentation of effective operating procedures
to define the processes and procedures for critical activities
serving as barriers to contamination; and (iii) operational control
measures and verification protocols to ensure that the barriers are
functioning effectively.
This approach offers Australia a rational and cost-effective
alternative to the excessively complex and costly regulatory
systems in the United States and Europe. Routine water testing for a
variety of chemical, physical and microbial parameters will remain
important for operational monitoring and verification of system
performance, but our drinking water supply will not be improved by
measuring for measuring's sake. There needs to be a very clear
rationale for testing drinking water and an understanding of what the
result of each measurement means. Testing is only one part of an
overall preventive strategy to ensure high quality drinking water at
an affordable cost.
Christopher K Fairley
Head, Infectious Disease Epidemiology Unit
Martha I Sinclair
Senior Research Fellow
Samantha Rizak
Research Fellow
Cooperative Research Centre for Water Quality and Treatment
Department of Epidemiology and Preventive Medicine
Monash
University, Monash Medical School, Alfred Hospital, Melbourne, VIC
christopher.fairleyATmed.monash.edu.au
- Surveillance for waterborne disease outbreaks -- United States,
1995-1996. MMWR Morb Mortal Wkly Rep 1998; 47(SS-5): 1-34.
-
Indicator organisms and the coliform concept. In: Gleeson C, Gray
N, editors. The coliform index and waterborne disease. London: E&FN
Spon (Chapman & Hall), 1997: 38-59.
-
National Water Quality Management Strategy: Australian Drinking
Water Guidelines. National Health and Medical Research Council
(NHMRC), Agriculture and Resource Management Council of Australia
and New Zealand (ARMCANZ). Canberra: NHMRC/ARMCANZ, 1996.
-
Sinclair MI, Fairley CK, Hellard M. Protozoa in drinking water: is
legislation the best answer? Med J Aust 1998; 169: 296-297.
-
Public health and drinking water: preventing Cryptosporidium
getting into public drinking water supplies. Consultation paper.
London: Department of the Environment, Transport and the Regions;
May 1998.
-
Wheeler JG, Sethi D, Cowden JM, et al. Study of infectious
intestinal disease in England: rates in the community, presenting to
general practice, and reported to national surveillance.
BMJ 1999; 318: 1046-1050.
-
National Health and Medical Research Council (NHMRC) and
Agriculture and Resource Management Council of Australia and New
Zealand (ARMCANZ). National Water Quality Management Strategy.
Revised Australian Drinking Water Guidelines. Draft -- July 1999.
Available from: <http://www.nhmrc.health.gov.au/
advice/water.htm> (accessed 16 September 1999). No longer available, but see revised and updated version at http://www.health.gov.au/hfs/nhmrc/publicat/synopses/eh19syn.htm Accessed 10 May
©MJA 1999
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