Supplying highly treated reclaimed water directly to a drinking water distribution system is known internationally as direct potable reuse (DPR). This differs from more established approaches to potable water recycling by the absence of a so-called ‘environmental buffer’, a practice referred to as indirect potable reuse (IPR). IPR involves the storage of treated reclaimed water in environmental buffers – such as a river, lake, reservoir or aquifer – prior to it being recovered through drinking water treatment plants and distributed to consumers.
To ATSE’s knowledge at the time of publication, there are no currently operating DPR projects in Australia and no specific proposals for their development. However, ongoing interest in sustainable water supply systems, advances in the science and engineering of water treatment, and recent international developments in DPR have prompted consideration of DPR as a potential future component of Australian water supply systems.
Any DPR scheme, as considered in this report, includes a number of general characteristics. A source of municipal wastewater is required, such as effluent from wastewater treatment plants, which is purified using advanced water treatment processes to effectively and reliably remove hazardous substances including pathogens and toxic chemicals. It would not be possible to meet all demand for drinking water through recycling, so the use of additional water sources remains essential. Finally, most DPR projects require a means of blending the recycled water with conventionally sourced water prior to delivery to consumers. Conceptually, DPR can be developed in a number of alternative configurations which differ by their arrangement of the water sources, treatment processes and blending locations.
The major difference between DPR and IPR, i.e. the use of environmental buffers, has been attributed a number of important functions. These include: additional treatment of pathogens and chemical contaminants; the provision of ‘time to respond’ to potential water treatment incidents; and improvement of public perceptions of potable water reuse. In order to maintain appropriate levels of safety, reliability, and public acceptance, such functions would need to be performed in any DPR system by engineered or other processes. This requires sophisticated approaches to water quality monitoring techniques, process reliability assessment, personnel training, engineered water storage design, and community engagement in particular.
It is instructive to observe that there are a number of successfully operating DPR schemes internationally. The most established of these has been operating in Namibia since 1968 without observed negative impacts to public health. More recently, DPR projects have been developed in the US and South Africa, with both countries now actively considering additional developments within the next few years. Recent Guidelines for Water Reuse developed by the US Environment Protection Agency state that “While DPR is still an emerging practice, it should be evaluated in water management planning, particularly for alternative solutions to meet urban water supply requirements that are energy intensive and ecologically unfavourable”. The State of California, in particular, is currently investigating the feasibility of developing uniform criteria for DPR.
Potential benefits of DPR, relative to IPR, are likely to be highly case-specific. However, potential benefits include significantly lower energy requirements, construction costs, and operational costs. DPR can also provide an opportunity to allow potable reuse in situations where a suitable environmental buffer is not available for IPR.
Potential obstacles or disadvantages for DPR, relative to IPR, are primarily related to public perception and acceptance. Importantly, ATSE considers that the scientific and engineering hurdles to implementing safe and reliable DPR are manageable. However, a number of technical issues relating to the functions of an environmental buffer in IPR are described above and would need to be addressed to the satisfaction of the general community. Key among these issues is the need to ensure reliability.
It is apparent from a review of Australian legislation and regulations that existing frameworks for the planning, approval, management, and oversight of drinking water quality and recycled water in Australia could accommodate a well-designed and operated DPR project as a water resource management option. Advanced risk assessment and risk management tools are now available which can be considered for the implementation of DPR projects, relative to more established or conventional water sources.
Related identifier: ISBN 978 1 921388 25 5