Health Stream Literature Summary - Issue 55 - September 2009

Indirect potable reuse: A sustainable water supply alternative.
Rodriguez, D., Van Buynder, P., Lugg, R., Blair, P., Devine, B., Cook, A. and Weinstein, P. (2009) International Journal of Environmental Research and Public Health, 6(3); 1174-1209.

There is a growing need to manage water resources in a sustainable manner in view of climate change, population growth and water scarcity in many areas of the world. Water recycling is becoming more important as one possible method of addressing water shortages, and the costs and energy requirements for indirect potable reuse (IPR) are declining as technology develops. In IPR, municipal wastewater is highly treated and discharged directly into groundwater or surface water sources with the intention of supplementing drinking water supplies. IPR can provide a source of water which does not depend on rainfall, and high quality recycled water that complies with drinking water standards and guidelines can be produced. This paper presents a state of the art review of planned water recycling for drinking purposes.

IPR has been successfully implemented in the United States (US), Europe and Singapore. There are 14 well-documented IPR projects around the world, with the longest established schemes being located in the US. In Australia there are some projects which are considering the use of IPR through aquifer recharge or dam supplementation, but as yet none are implementing potable reuse. IPR has been proposed for Toowoomba (Queensland), Perth (Western Australia), Goulburn (New South Wales) and South East Queensland.

A small number of published epidemiological studies have examined the possible health impacts of potable reuse schemes on human populations. None have reported adverse health impacts despite variations in treatment technologies, environmental buffers, proportions of recycled water blended with raw drinking water sources (from 1% to 100%) and estimated retention times in the receiving waters (from 40 days to several years). Most studies have been ecological in design and thus could not accurately assess water exposure or take account of the many other factors which may have affected the health outcomes examined. One cohort study examined the association between the use of recycled water and adverse birth outcomes from 1982 to 1993, and did not find any significant association. A report on potable reuse published in 1998 by the US National Research Council concluded that, from the available information, the risk from IPR projects were similar to or less than the risks from conventional water sources, however a recommendation was made that IPR should be an option of last resort.

Toxicological studies examining the effect of feeding concentrates of recycled water to test animals have overall found no significant health risks. The most extensive studies have been performed for demonstration projects in Denver and Tampa USA, and the IPR scheme in Singapore. Tests have included sub-chronic and chronic exposures, as well as reproductive, developmental and carcinogenic outcomes in multi-generational studies in rodents (and also fish in Singapore). No adverse effects have been reported in these studies. Mutagenic studies have been performed for several US sites and in general recycled waters have demonstrated less mutagenic activity than other water sources. Bioassays for oestrogen, androgen and thyroid activity have shown very low endocrine activity in the final product water.

To ensure public health protection a variety of factors need to be assessed for IPR projects, including the treatment processes required to achieve high water quality; the quality of the existing water supply and any changes after recycled water is blended; system reliability and the regulatory framework and risk management practices. By examining existing IPR projects, knowledge can be gained about some of the fundamental practices and lessons learned from their implementation. Extensive monitoring schemes have demonstrated that the multi-step water treatment processes used in IPR can consistently produce water meeting all primary and secondary drinking water standards. The quality of treated water is equal to or better than that of the existing untreated or treated drinking water supplies. However the large range of chemical contaminants in wastewater also requires that additional monitoring for a range of chemicals is performed to ensure these do not pose a health risk. Reliable removal of faecal pathogens is also required. A multiple barrier approach is needed for IPR as for conventional drinking water treatment. This approach includes source control, use of multiple water treatment processes, use of environmental buffers and conventional drinking water treatment to ensure that there are several independent steps in place to remove contaminants as no single barrier is able to remove all contaminants from wastewater.

Different jurisdictions have developed different approaches to regulation of IPR projects. Risk management frameworks are often applied to ensure the risks are minimal and final product water is of the best quality. Some of the more common approaches include: Best Available Technology, Life Cycle Analysis, and Hazard Analysis and Critical Control Points (HACCP). Typical treatment requirements include advanced treatment of secondary sewage effluent using microfiltration and/or reverse osmosis filtration and in some cases also UV irradiation and/or advanced oxidation processes to remove chemical and biological hazards. This is coupled with conformance with drinking water guidelines in the product water, extensive monitoring for known or suspected contaminants and minimum residence time in the receiving aquifer or surface water body. Other requirements include monitoring and site-specific controls on the operation, maintenance and management of the plants.

More research is needed to identify new potential contaminants of concern in recycled water and also to develop validated methods for detection of emerging and other unregulated contaminants. Implementation of IPR also requires integration of regulatory approaches for recycled water and drinking water to protect health. Well-coordinated public health surveillance systems are also needed to document possible warning signs of any adverse health events association with recycled water ingestion.

Research into community attitudes to recycled water has identified a number of factors which affect acceptance and support. These include the degree of water scarcity, the supply costs, the quality of the consultative processes, the perceived management of health risks and the accountability of, and trust in, the regulator, the government and the water utility. Additional targeted social research is needed in communities where IPR is proposed.

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