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Proper water management requires recycling as well as conservation

By Greg Leslie - posted Thursday, 29 April 2004

With storage levels in Sydney's main dam hovering near 50 per cent it is welcome news that plans have been tabled to augment Sydney's water supply by up to 25 per cent.

However, transferring water from distant catchments and upgrading pumping equipment to access deeper levels of existing storages might not offer the long-term solution that Sydney needs.

It's worth considering plans recently implemented by areas with demographics not dissimilar to Sydney: both the island republic of Singapore (population 3.5 million) and Orange County in Southern California (population 2.3 million) are growing urban centres with expanding industries, populations and house prices. Like Sydney, both Singapore and Orange County faced uncertain water futures.


More than a half of Singapore's water falls in catchments in Malaysia and arrives via large pipes. More than 25 per cent of Orange County's water supply begins life as snow melt in either the Colorado Rockies or in the Sierras of northern California.

In both cases treaties and agreements ensure current supplies, but neither Singapore nor Orange County hold much prospect of securing more water to meet future demands.

Reasons for the uncertainty vary. In Singapore, historical tensions with Malaysia, which controls the tap, must be carefully negotiated. In Southern California, hostile neighbours to the east in Arizona and in northern California also seek to turn off the tap. In the east, Arizona will reduce California's access to the Colorado river courtesy of a US Supreme court ruling which caps California's entitlement. In northern California, environmental interests are seeking to reduce the flow of fresh water to Southern California, partly to protect 22 endangered fish and bird species.

Although conditions in Singapore and Orange County are different to Sydney, we could learn from the strategies they have adopted. Both Singapore and Orange County have developed solutions based on demand management and diversification of water sources. The notion of demand management is not earth-shattering. Water is a precious resource that should not be wasted or used in an "unreasonable" way. A unique feature of the California state constitution is the uniform prohibition on the wasteful use of water.

It is encouraging that the NSW government has set a target of 40 per cent reduction in water consumption for new developments and utilities are encouraging the use of water saving devices in the home. But NSW has a long way to go: Singapore's per-capita water consumption is 170 litres per person per day; Sydney's is 380 litres.

Singapore and Orange County both acknowledge that conservation is not enough. Both Singapore and Orange County have made a commitment to maximise the use of available freshwater by aggressive recycling schemes which aim to capture millions of litres of waste water that is pumped into the ocean.


Using a system based on the human body's own kidneys - which are the ultimate in water recycling technology - Singapore and Orange County have developed schemes that will use a dual membrane process to recycle domestic wastewater (sewage) to levels that approach the quality of distilled water. Like the kidney, these recycling plants use two membranes, one with larger holes to remove microorganisms like protozoa and bacteria that cause infection, while the second separates salt from water.

Singapore has already built three plants and has plans to build a fourth which will recycle 20 per cent of water discharged into the ocean. The water, at almost distilled quality, makes it very appealing for high tech semi-conductor manufacturers who need very pure water for the process. Water that is not used by industry is delivered to the island's reservoirs where it sits for six months before being treated again at a drinking water plant before making its way back into the water supply.

Similarly, by 2006 Orange County will have commissioned one large recycling plant that will treat the municipal wastewater before it is used to recharge natural ground water supplies. Again, the recycled water will mix with existing supplies for six moths to a year before it is pumped to the surface, treated and delivered through the water distribution system. Orange County’s recycling scheme provides a renewable source of water that can be produced for about one half of the energy required to pump an equivalent volume of water from the Colorado river.

The raw cost to treat and recycle water using the dual membrane process is about $0.55 per kilolitre on top of the cost of treatment to secondary effluent standards. (Sea water desalting techniques, the ultimate alternative water source, cost about $1.40 per kilolitre.) The NSW government, to its credit, has built similar recycling schemes at Sydney Olympic Park and Port Kembla, albeit 20 times smaller. However, there has not been a big push to maximize this form of recycling. Such schemes are ambitious, controversial and possibly unpalatable - although residents of London are used to the idea of drinking water from the Thames that has been recycled several times by communities upstream.

With other projects competing for the public dollar, large scale recycling projects often get placed in the too hard basket. Water recycling in itself is not a panacea, and cannot replace demand management, however, recycling can make water resources go further without damaging the environment. As for water transfers, experience elsewhere and increasingly in Sydney tells us we can't always rely on water that falls in our neighbor's garden.

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This article first appeared in The Sydney Morning Herald on 19 April 2004.

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About the Author

Associate Professor Greg Leslie is an associate professor at the University of NSW's UNESCO Centre for Membrane Science and Technology.

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