news, water-pressure, water pressure, stuart khan, water recycling
Safe drinking water is our most precious resource. But you wouldn't guess that by looking at how most cities manage water. We capture it in dams, then use it once before discharging it out to sea. If we really valued a resource, especially one prone to shortages, we would hold on to it. We would do what we could to reduce, reuse and recycle. Reducing water consumption is something we have gotten much better at. Many homes now have dual-flush toilets and low-flow showerheads. Our clothes washers and dishwashers are more water-efficient than they were 20 years ago. During times of water restrictions, Australians have proved themselves to be very effective at cutting back on outdoor water use. Reusing water has also come a long way. Some water from sewage treatment plants is now reused to irrigate open space. There's hardly a town in NSW that isn't reusing some treated sewage effluent to irrigate a golf course. Many also irrigate playing fields, parks and municipal gardens. A few cities have small areas where treated sewage is reused on household lawns and gardens, as well as for flushing toilets. To keep this reclaimed water segregated from drinking water, it is delivered in a separate pipe network, which is usually painted purple, to indicate that the water is not suitable for drinking. All of these efforts to reuse water are good and they all help. But these approaches are limited in the amounts of water that they can supply and the amounts of fresh water use that they can replace. Reusing water for irrigation is limited by the weather. Golf courses, playing fields, parks and gardens will use the water when the weather is dry. But unless very large storage is available, which it rarely is, this water will be discharged when its raining and the ground is wet. There are reasons why purple-pipes will only ever be a niche solution for small new development areas. One is that they are effectively impossible to retrofit to older suburbs, so they only apply to greenfield sites. Furthermore, they're rarely cost-effective. The high level of treatment needed, and the whole separate water supply system tend to costs more per litre of water than customers pay for drinking water, - usually less than 0.3c per litre. Like all irrigation, customer demand for purple-pipe water is seasonal. Most use is for garden watering, which is heavy in summer, but much less in winter. A system that can supply a set volume of water will either run short in summer or have too much water in winter. In some areas, this has been managed by topping-up purple-pipe water supplies with drinking water during summer. Limiting their potential benefit further, areas with purple-pipes are generally not effective at saving additional water with rainwater tanks. The purple pipes are used for watering lawns and gardens, meaning that there's little remaining use for rainwater. But there is a way in which cities can maximise the water supply benefits available from treated wastewater. That is to treat the water to a sufficiently high quality that it can be safely and reliably used as additional drinking water supply. This approach is truly 'recycling' since the water follows an identifiable 'cycle' rather than a linear chain of more limited uses. RELATED READING Digging deep to find solution Water Pressure: Water regulation not keeping up Policy makers scramble to ensure the Hunter has a reliable and sustainable water supply For excellent examples on how to recycle water, we don't need to look far. Perth began water recycling in 2017 with the establishment of the 'Groundwater Replenishment Scheme'. Water from a sewage treatment plant is highly purified by advanced water treatment processes before being pumped underground to the groundwater system, which forms an important part of Perth's drinking water supply. A very large water recycling scheme was also constructed in Brisbane towards the end of the Millennium Drought. Known as the 'Western Corridor Recycled Water Scheme', it consists of three advanced water treatment plants that can purify the treated effluents from almost all of Brisbane's sewage. The highly purified recycled water is then suitable to top-up Brisbane's largest drinking water supply, Lake Wivenhoe. Soon after the Western Corridor Recycled Water Scheme was built, the drought broke and Lake Wivenhoe filled to overflowing. So the project was mothballed and hasn't yet been used as a drinking water supply. However, once the storage levels drop to below 60 per cent of capacity, it will be restarted and, when ready, will supply recycled water for Brisbane. If we plan carefully, water recycling can provide a highly reliable, relatively drought resistant supply of safe, clean drinking water to our cities. In many cases, it can be done at lower cost, lower energy and lower carbon footprint than seawater desalination. Its an option that should be on the table and carefully considered by all Australian cities.
NEED IS CLEAR: Finding better ways to improve urban water security is crucial, Dr Stuart Khan says.
Safe drinking water is our most precious resource.
But you wouldn't guess that by looking at how most cities manage water. We capture it in dams, then use it once before discharging it out to sea.
If we really valued a resource, especially one prone to shortages, we would hold on to it. We would do what we could to reduce, reuse and recycle.
Reducing water consumption is something we have gotten much better at. Many homes now have dual-flush toilets and low-flow showerheads. Our clothes washers and dishwashers are more water-efficient than they were 20 years ago. During times of water restrictions, Australians have proved themselves to be very effective at cutting back on outdoor water use.
Reusing water has also come a long way. Some water from sewage treatment plants is now reused to irrigate open space. There's hardly a town in NSW that isn't reusing some treated sewage effluent to irrigate a golf course. Many also irrigate playing fields, parks and municipal gardens.
A few cities have small areas where treated sewage is reused on household lawns and gardens, as well as for flushing toilets. To keep this reclaimed water segregated from drinking water, it is delivered in a separate pipe network, which is usually painted purple, to indicate that the water is not suitable for drinking.
For excellent examples on how to recycle water, we don't need to look far.
All of these efforts to reuse water are good and they all help. But these approaches are limited in the amounts of water that they can supply and the amounts of fresh water use that they can replace.
Reusing water for irrigation is limited by the weather. Golf courses, playing fields, parks and gardens will use the water when the weather is dry. But unless very large storage is available, which it rarely is, this water will be discharged when its raining and the ground is wet.
There are reasons why purple-pipes will only ever be a niche solution for small new development areas. One is that they are effectively impossible to retrofit to older suburbs, so they only apply to greenfield sites. Furthermore, they're rarely cost-effective. The high level of treatment needed, and the whole separate water supply system tend to costs more per litre of water than customers pay for drinking water, - usually less than 0.3c per litre.
Like all irrigation, customer demand for purple-pipe water is seasonal. Most use is for garden watering, which is heavy in summer, but much less in winter. A system that can supply a set volume of water will either run short in summer or have too much water in winter. In some areas, this has been managed by topping-up purple-pipe water supplies with drinking water during summer.
Limiting their potential benefit further, areas with purple-pipes are generally not effective at saving additional water with rainwater tanks. The purple pipes are used for watering lawns and gardens, meaning that there's little remaining use for rainwater.
But there is a way in which cities can maximise the water supply benefits available from treated wastewater. That is to treat the water to a sufficiently high quality that it can be safely and reliably used as additional drinking water supply. This approach is truly 'recycling' since the water follows an identifiable 'cycle' rather than a linear chain of more limited uses.
For excellent examples on how to recycle water, we don't need to look far. Perth began water recycling in 2017 with the establishment of the 'Groundwater Replenishment Scheme'. Water from a sewage treatment plant is highly purified by advanced water treatment processes before being pumped underground to the groundwater system, which forms an important part of Perth's drinking water supply.
A very large water recycling scheme was also constructed in Brisbane towards the end of the Millennium Drought. Known as the 'Western Corridor Recycled Water Scheme', it consists of three advanced water treatment plants that can purify the treated effluents from almost all of Brisbane's sewage. The highly purified recycled water is then suitable to top-up Brisbane's largest drinking water supply, Lake Wivenhoe.
Soon after the Western Corridor Recycled Water Scheme was built, the drought broke and Lake Wivenhoe filled to overflowing. So the project was mothballed and hasn't yet been used as a drinking water supply.
However, once the storage levels drop to below 60 per cent of capacity, it will be restarted and, when ready, will supply recycled water for Brisbane.
If we plan carefully, water recycling can provide a highly reliable, relatively drought resistant supply of safe, clean drinking water to our cities. In many cases, it can be done at lower cost, lower energy and lower carbon footprint than seawater desalination. Its an option that should be on the table and carefully considered by all Australian cities.
Dr Stuart Khan is a professor of civil and environmental engineering at UNSW
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