Population growth and urban densification are placing additional stress on urban water supplies. Are we ready to have the debate on potable reuse of recycled water?
Population growth and urban densification are placing additional stress on urban water supplies and networks. As urban centres continue to grow, it is inevitable that traditional water sources such as managed catchments and groundwater will need to be supplemented to an increasing degree by climate-independent sources. Potable reuse of recycled water is a technically feasible option that is climate-independent and has a lower cost than other alternatives (such as desalination), but public acceptance is not well advanced. So are we ready to have the debate on potable reuse of recycled water?
With population growth and urban densification, an increasing proportion of our water supplies will need to be secured from climate independent supplies such as seawater desalination and water recycling. For Australia’s urban centres, this statement is reinforced with the fact that Australia is not only the driest inhabited continent, but one with very strong year-to-year rainfall variability. The recent announcement by the Australian Bureau of Meteorology that the El Nino Southern Oscillation (ENSO) Index has triggered the threshold indicating El Nino conditions, raises the probability of lower than average rainfall in Eastern Australia and the risk of drought conditions again.
While desalination and wastewater recycling schemes produce water at a higher unit cost than catchment or groundwater-derived supplies, they are much more reliable given they are independent of rainfall, continuing to provide essential water when the reservoirs run dry or when floods or fires make surface water unusable. Storm water recycling has low drought reliability and its water supply security benefit is contingent upon continued use during normal climatic conditions, preserving stored water for drier conditions. Aquifer storage and recovery of recycled water is another option that can be used where geology and groundwater conditions are suited.
Singapore uses the concept of "Four National Taps" to convey its water security strategy: catchment supplies (both natural catchments and urban storm water catchments), seawater desalination, wastewater recycling for indirect potable use, and water imported from neighbouring Malaysia. The Australian urban water industry has widely adopted the first two "taps", which are catchment supplies and seawater desalination.
Australia invested heavily in water security works over the latter period of the Millennium Drought (1997 to 2009), with seawater desalination plants designed and built in each mainland State, and numerous water recycling schemes commissioned for both non-potable and potable use. The decisions made to invest in these schemes generated much debate at the time, particularly when drought conditions eased with several plants still under construction. However, the reality is that planning, designing, constructing and commissioning a large desalination plant or water recycling scheme takes many years - in the order of six to ten years for a large scheme. One of the lessons from the Millennium Drought was that making decisions under emergency conditions is unlikely to achieve optimal outcomes.
South East Queensland built the Western Corridor scheme for potable reuse, although the scheme was shutdown in mid-2013 as reservoirs levels rose and the political will to use the scheme was drowned by public concerns. Many other wastewater recycling schemes have been built for non-potable reuse with supply largely to new residential developments through a dedicated "third pipe” network for garden and toilet flushing. The cost of constructing the third pipe network is very high, and is often borne by developers and passed on to new home buyers.
Public acceptance of potable re-use, and the will of governments to propose it, is not well advanced. Recycled water can be produced at a lower cost and with less energy than desalinated seawater. Potable re-use of recycled water has a significant advantage over non-potable domestic reuse in that it does not require additional investment in a separate 'third pipe' network. Water recycling is also compatible with the growing interest in resource recovery (energy, nutrients) from wastewater and the concept of a circular water economy. With increasing pressure from the community for lower utility bills, potable reuse should be on the table for consideration.
With El Nino conditions back, the next drought of the millennium may or may not be upon us, but it is not too soon to start planning for it. So what are the next steps?
- Potable reuse needs to be embraced in policy and regulation, removing regulatory impediments well ahead of any emergency situation
- Public debate and education is needed to raise awareness of the need for climate-independent water sources and the benefits of a circular water economy with urban water managed as a fully reusable resource
- Although the technology is proven, building and operating trial facilities where recycled water can be introduced as a small proportion of a water supply system will build confidence in the technology.
Potable reuse of recycled water is an inevitable part of our urban water future. However, the timeframe to implement such schemes is long, and the planning must not be left until emergency conditions occur. Now is the time to build on the lessons of the millennium drought so that when Australia enters the next big dry, we are better prepared for the inevitable.