When Australia last experienced an El Niño event, cities like Brisbane, Sydney, Canberra, and Melbourne faced significant water supply issues. With the recent wet La Niña years, one might assume that we are better prepared for future challenges. However, the situation is not that simple. For instance, Sydney’s dams are currently at around 90% capacity, holding four times the amount of water consumed in a year. Yet, hot and dry weather can quickly deplete these reserves due to increased demand, evaporation, and reduced replenishment from rivers like the Nepean. Additionally, high temperatures dry out the soil in water catchments, hindering runoff into waterways. To address this vulnerability and secure a reliable water supply in the face of climate change, Sydney needs to explore alternative sources of water, such as desalination plants and recycling schemes.
In 2010, Sydney’s first large-scale seawater desalination plant began operating. With a maximum production capacity of 90 gigalitres per year, it can meet approximately 15% of the city’s annual water demand. Historically, the desalination plant has been turned off and on based on rainfall levels. For instance, when the dams reached 90% capacity in 2012 after the Millennium Drought broke, the plant was deactivated. However, during the recent drought, it was reactivated in 2019. The drawback of this approach is that it takes months to restart a mothballed desalination plant. To optimize its benefits, desalination plants should be operational continuously at a low rate to ensure a more prompt response during water shortages. Sustained operation also allows for the maintenance of the necessary workforce and skills to operate the plant effectively.
While several Australian cities have invested in desalination plants, fewer have explored purified water recycling from wastewater treatment plants due to unwarranted public skepticism. Perth’s groundwater replenishment scheme stands out as Australia’s most significant purified recycled water project. Starting in 2017, treated wastewater was purified and injected into an aquifer used for drinking water. Currently, this project provides about 10% of Perth’s drinking water demand annually. By 2035, the Water Corporation aims to recycle more than a third of treated wastewater, further reducing reliance on traditional water sources.
Queensland has also implemented a considerable water recycling scheme, the Western Corridor Recycled Water Scheme, although it remains underutilized. If fully utilized, it could contribute 80 gigalitres per year to the water supply of South East Queensland’s 3.8 million residents. This volume would be sufficient to replenish the region’s largest surface water storage, Lake Wivenhoe. Embracing purified recycled water as a viable option can diversify Sydney’s water sources and reduce dependence on rainfall.
Sydney currently depends on rainfall-dependent sources to fulfill approximately 80% of its drinking water supply. The Greater Sydney Water Strategy warns that continued dry conditions could lead to water shortages within three years. To prevent such a scenario, it is crucial to develop additional rainfall-independent water supplies that guarantee full dams at the onset of droughts and allow for a more measured response to water scarcity. This calls for expanding existing desalination plants, constructing new ones, and scaling up purified recycled water initiatives. Each option comes with its own costs and benefits, necessitating careful consideration and a holistic approach.
Rather than choosing between desalination plants and purified recycled water, Sydney needs to adopt a diversified approach that incorporates multiple water sources in different areas of the city. This approach acknowledges the limitations of the water supply network and ensures that water can be delivered efficiently to specific locations. It is not a matter of selecting one option over the others but determining the most effective order of implementation.
Sydney must proactively tackle its water supply challenges by developing a comprehensive and multifaceted strategy. While the La Niña years have provided temporary relief, the city cannot rely solely on climatic patterns to secure its water future. Implementing a mix of desalination plants and recycled water initiatives will enhance resilience, reduce reliance on rainfall, and ensure a consistent supply of water for its growing population. By adopting this holistic approach, Sydney can overcome future water shortages and emerge as a model for sustainable water management.