Can health-based targets fill the gaps in current water quality guidelines?

Although most of the Australian Drinking Water Guidelines (ADWG) provide a solid definition of safe, good-quality water, the definition of microbial safety is currently arbitrary and lacks quantitative standards.

So argues Dr Michael Lawrence, water systems auditor at consultancy Bligh Tanner, and for this reason he is supporting the integration of health-based targets (HBT) into the ADWG.

In the early 2000s, Australia pioneered a risk-based approach to boost drinking water quality management that relied on sampling water at various stages of the treatment process.

Using this approach potential hazards to water quality are identified by analysing data to compare the quality of the source against water at various stages of treatment. This technique also considers the effectiveness of the treatment plant under normal conditions versus extreme events, such as heavy rainfall.

This data enables treatment plant operators to determine the level of risk associated with each contaminant, and potential areas for improvement within the treatment plant.

However, water quality sampling is often infrequent – some small utilities might only take verification samples once per month, and therefore it might not be possible to determine what needs improvement based on the locations of the samples.

Furthermore, in some cases the operational monitoring is also not sufficient.

“Many smaller regional water suppliers do not have online turbidity monitoring for their filters, let alone individual meters on each filter”, said Lawrence, who will be presenting on health-based targets and risk assessment at the upcoming North Queensland Regional Conference.

This puts the safety of the water at risk, as insufficient filtration might result in parasites such as Cryptosporidum passing through the filters and into the drinking water supply.

Lawrence explained that this inability to measure functionality of the filters prevents providers from proving that Cryptosporidium risk has been reduced. If there is a demonstrated Cryptosporidium risk in the catchment, and the filters are unable to remove them, that leaves the water almost “unquestionably unsafe to drink”.

This is compounded by gaps currently in the application of the ADWG within current jurisdictions that address quantitative standards, leaving individual operators to judge which treatments are sufficient and effective enough.

To combat this, Lawrence supports the introduction of health-based targets to be included in the ADWG.

The aim of these HBT is to help define the tolerably low risk for microbial infection in drinking water, and use data compiled at various stages of the treatment process to ensure that the microbial load is being reduced sufficiently for the HBT to be met. The HBT can also be used to determine where improvements in the treatment plant need to be made.

“The identification of a shortfall is a first step for providers acknowledging that there is a need for spending significant money on treatment plant upgrades [or identifying alternate options],” Lawrence said.

“Where a supply is unsafe, water managers will need to communicate their recommendations upwards to councillors regarding the need for critical upgrades, but also down to the operators to ensure that every possible improvement of current practice can be made.”

The HBTs are calculated based on disability adjusted life years (DALY), which accounts for the risk, severity, duration and impacts of disease.

Using this scale, one DALY is equal to one lost year of healthy life per person. Australia has adopted an HBT of 10-6 DALYs per person per year, or one case of diarrhea per 1700 people per year. This is in line with the value adopted by the World Health Organisation (WHO).

Although it’s impossible to achieve zero risk associated with drinking treated water, the HBT can define a point where the risk to consumers is acceptably low and can unquestionably be considered safe to drink.

“The idea of the HBT is to ensure that we prevent disease outbreaks from occurring by taking all reasonable steps to avoid them,” Lawrence said.

“In many cases that we are talking about, you might be able to argue that the providers are not yet providing drinking water to an adequate standard.”

For more information about how applying the HBT to the ADWG can help significantly improve water quality and safety, see Michael Lawrence, Sean Hinton and Nicholas Wellwood present at the North Queensland Regional Conference. To learn more and to register, click here.