Water demand driven by population growth is surpassing the gains made in Australians’ household water use efficiency, according to a new report from Sustainable Population Australia (SPA) titled Big Thirsty Australia: How Population Growth Threatens Our Water Security and Sustainability.

The report highlights that, since 2010, individual household water use has remained relatively constant. Dr. Peter Cook, one of the report’s authors, explains that further improvements are becoming increasingly difficult as most straightforward solutions—such as public education campaigns, water-efficient appliance labeling, and reduced garden sizes—have already been implemented.

The findings indicate that population-driven demand is coinciding with climate change impacts, which are reducing water availability in capital city catchments on the world’s driest inhabited continent. These combined pressures are making Australian cities more susceptible to prolonged droughts.

Since the early 2000s, water demand in many urban areas has exceeded the capacity of traditional sources like rainfall and groundwater, notes Dr. Jonathan Sobels, another author of the report.

The report also reveals that urban water authorities in mainland Australia project that population growth will necessitate an additional 850 to over 1450 gigalitres (GL) of annual water supply for capital cities in the coming decades. To put this into perspective, 1450 GL is approximately the combined annual water supply currently provided to Sydney, Melbourne, and Perth.

Reliance on seawater desalination

In response, state governments and water utilities are increasingly relying on seawater desalination to meet the growing demand. However, desalination is costly, with expenses per litre at least 2.5 times higher than water from rain-fed dams, leading to significantly higher household and business water bills. Furthermore, desalination is energy-intensive, with electricity accounting for about 41% of its operational costs. Even when renewable energy is used, it does not necessarily reduce the overall carbon footprint due to the displacement of fossil fuels in other sectors. Coastal desalination plants are also at risk from rising sea levels linked to climate change, Sobels warns.

SPA national president Peter Strachan points to government projections that Australia’s population will grow by another 13 million over the next 40 years. He argues that the high costs of desalination could be avoided by stabilizing the population.

“Population growth is the primary driver of increased water demand. Relying on desalination to support continued population growth adds new risks to water security and further harms the environment,” Strachan states.

The report also challenges the acceptance of population growth projections dictated by the federal Treasury, which leave state and local governments responsible for funding infrastructure and securing additional water supplies. Strachan emphasizes that population growth is a policy choice, not an inevitability.

He advocates for reducing annual net migration to pre-2005 levels of around 70,000. This would allow investments to focus on upgrading ageing water infrastructure, greening cities, and restoring wetlands, rather than accommodating unsustainable growth.