Recycled water – safe or not?
The biggest breakthrough in improving human health has been providing drinking water that has been separated from waste water. There are nasties in the gut that we do not want to circulate in our drinking water. Checking that our drinking water is clean and safe to drink has been mainly by checking on the presence or absence of E. coli but has now been superseded by a preventive risk management approach. Water shortages and a need to use recycled water has prompted a big push to improve the tools needed to ensure our drinking water is safe.
Essential first steps are providing a quantifiable definition of safety. Which is based on recognising that not all pathogens are created equal, some only cause mild diarrhoea while others such as E. coli 0157 can cause more severe symptoms including haemolytic uraemic syndrome and death. And the definition of safety provides the goalposts that need to be achieved. using a risk management system. For use of recycled water include either reducing pathogen concentrations using treatment OR by reducing exposure through mechanisms such as how the water is used (eg, drip versus spray irrigation), applying buffer zones between points of use, and public access or crop restrictions (eg, irrigation of fruit trees rather than lettuce).
The guidelines describe typical reductions achieved by various types of treatment and exposure controls. This dual approach means that even sewage with relatively low levels of treatment can be used safely, provided appropriate end-use or on-site restrictions are applied. However, high-exposure uses such as dual reticulation will always rely on high levels of treatment.
In the risk management approach, monitoring focuses on checking that control measures work effectively. It relies on recoding contact time with chlorine which correlates with inactivation of enteric bacteria and viruses and removing turbidity by filtration correlates with removal of particles such as Cryptosporidium. The advantage of this approach is that the indicators can be measured continuously using automatic monitoring devices connected to alarm systems rather than relying on sampling.
This is based on a much more detailed paper by David Cunliffe provided courtesy of The Australian Society for Microbiology.
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