THE WATER SAFETY CONTINUUM
A PRACTICAL WAY TO IMPLEMENT A HEALTH-BASED TARGET FOR MICROBIAL WATER QUALITY
Publication Date (Web): 12 February 2016
Best practice for managing drinking water quality is now accepted to be the use of Health Based Targets (HBTs). This approach is based on the fact that pathogenic microorganisms pose the greatest risk of water-borne disease, and that assessing and managing that risk holds the key to controlling water quality.
The introduction of a HBT for microbial water quality in Australia has the potential benefi t for water providers of providing a mechanism for determining the adequacy of water treatment processes and setting consistent operational performance targets. The most likely HBT to be adopted is the World Health Organisation (WHO) target of one micro DALY PPPY.
This is the best metric to quantify disease burden, but it is a diffi cult concept to understand, and there is no ‘feel’ currently for the consequences if the HBT is not met. The water industry can appreciate the advantages of a HBT, but has concerns about how it will be interpreted and applied by health and other regulators in Australia.
In 2012, WSAA set up a working group to advise on the use of HBTs. The group developed a concept known as the Water Safety Continuum to improve drinking water quality outcomes for consumers and to help understand the consequences of not meeting the HBT.
The Continuum plots the incidence of community disease for alternative water safety outcomes and log removal shortfalls.
Context is provided by comparison with background GI (gastrointestinal disease) levels, the detection of outbreaks by health surveillance and well-known water quality incidents such as ‘Milwaukee’.
Bands of safety have been superimposed on the Continuum in recognition of the inherent uncertainty associated with water safety calculations. When considered in the context of the Continuum it is concluded that: achieving the HBT of one micro DALY PPPY means the drinking water is unquestionably safe; however, the converse is not true and, therefore, the HBT should not be considered a pass/fail metric; the HBT of one micro DALY PPPY should be retained as an aspirational target, while remaining cognisant that it cannot be verifi ed by health surveillance.
The HBT is best used in conjunction with the Water Safety Continuum as a benchmarking tool – it indicates the quantum and type of improvements required, so is a valuable tool to manage utility water quality improvement programs. The further to the left a scheme is located on the Continuum, the more significant and urgent is the improvement required; the Continuum can be used to link the operation of catchments and water treatment plants to public health outcomes. Operators can appreciate the public health impacts of their day-to-day decisions and the Continuum can also be used as a tool to help with the management of water quality incidents. The development of the Continuum has provided confidence that a HBT can be implemented in a pragmatic fashion in Australia.
If adopted, the benefits of a consistent approach to water treatment adequacy can be achieved without unwieldy and impractical regulatory arrangements.
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