Water security: how does Melbourne meet its future water needs?

Sustainability Matters asked AECOM’s Water Resource Practice leader, Melanie Collett, about future urban water security challenges from a local perspective.

Is there a risk that there will be insufficient water supplies in Melbourne to meet the needs of the predicted future population growth? If so, when?

Melanie Collett (MC): The recently released Melbourne Water System Strategy suggests that water supplies will need to be supplemented sometime within the next 50 years to meet the growing population in Melbourne. Water supply is dependent on two things: the amount of water (supply) and the use of water (demand). Insufficient water supply occurs when the demand is greater than the supply.

There are many ways to mitigate this problem including increasing supply or decreasing demand. Melbourne’s current water is mostly sourced from rainfall in the water supply catchments, which is stored in our large reservoirs. One of the biggest risks to supply going forward is the impact of climate change, which may reduce runoff in the catchment, which may reduce water supplies. Land use changes such as urbanisation, natural rainfall variability (droughts) and degraded water quality (due to bushfires) can also impact on water supplies.

The demand for water increases with population growth, but can be reduced through education campaigns and the use of alternative water sources for non-potable water requirements such as toilet flushing and outdoor use.

On the supply side, alternative water sources may be used to supplement the current potable water from catchments. These alternative sources include desalination, stormwater harvesting and recycled water from treatment plants. With each of these alternative water sources, treatment is required to improve the quality of water to make it suitable for use.

When will we run out of water? — We can’t say for certain. This will depend on both the supply and demand of potable water. Water authorities such as Melbourne Water are constantly modelling different scenarios of both supply and demand to predict what could happen in the future and plan for any eventuality.

Monitoring of the catchment conditions, supply and demand against the plan can help decision-makers to refine the plans as changes become apparent. Implementation of the changes to the plans is required to ensure that we don’t run out of water.

How is climate change expected to exacerbate the demands on water resources and how can this be counteracted?

MC: Current science estimates that temperatures in Australia could increase by four degrees by 2100. This increase in temperature will cause many changes to our environment. These changes include drier soil conditions, increased evaporation and less rain in winter, which all lead to less runoff in the water supply catchments.

These same changes could lead to more bushfires. Bushfires can have significant impacts on water supply — including decreased water quality straight after a bushfire due to the ash. In the years after a bushfire, as the trees are recovering and regrowing, they need more water, which will reduce the amount of runoff in the catchment. Research indicates that it can take up to 100 years for water supply to return to pre-fire levels.

Other changes include more intense rain and sea-level rise, which both lead to more severe flooding in low-lying areas. This will cause more damage to infrastructure and risk to human life. For example, we currently build our houses above the 1-in-100 flood level, which is equivalent to a flood that occurs on average once every 100 years. By 2100, this flood level could be caused by a 1-in-20 or 1-in-50 flood, and we could have up to five of them every 100 years.

Higher temperatures also mean decreased water quality and more algae blooms. This is a risk to human health and can lead to more costly water quality treatment. Higher temperatures also lead to increased demand for water for drinking and recreation.

Sea-level rise will lead to higher groundwater levels and higher salinity in our soil and water. This can have several impacts including increased corrosion, which would lead to decreased asset life, which would increase the cost of maintenance of in-ground assets like sewers, drains and water supply pipes.

In Victoria, the water infrastructure sector is one of the largest producers of greenhouse gas emissions, the main cause of climate change. It is estimated that the sector contributes 24% of the total Victorian Government emissions.

The only way we can reduce the impacts of climate change is to reduce our greenhouse gas emissions. The Victorian Government has set a target of net-zero by 2050, with the potential to offset using carbon sequestration.

The catch-22 is that many water recycling options are energy intensive, which could increase greenhouse gas emissions. We need to find ways to integrate water-saving and energy-saving measures rather than looking at them in isolation, otherwise emissions could increase to meet higher water demand rather than reducing.

Another way that we can counteract the impacts of climate change is to reduce the losses in the water supply system. This includes reducing evaporation from open water storages, reducing transmission losses in open channels and reducing leakage in pipes.  Every bit of water that we can save will help make our water supplies last longer.

Do you think that technology could help to ensure Australia’s future water security? If so, how and what types of technology could be utilised by the water industry?

MC: Technology is critical in enabling the water industry to meet the future water supply and demand challenges. We need to find more efficient ways to do things. This means we need more data, more modelling and analysis, more research and smarter ways to treat water.

The biggest challenge going forward will be to improve water quality. Finding ways to treat stormwater and wastewater for re-use and recycling, using cost and energy-efficient methods.

What other types of solutions could be implemented to ensure Australia’s water security?

MC: Integrated solutions are required to address the issue of reduced supply and increased demand for water. The Victorian Government is investigating the best mix of legislative, regulatory, financial and market based incentives to do this. This includes the establishment of the Integrated Water Management Framework.

The traditional methods used by the water authorities to address water supply and demand problems won’t be effective in the future.  The water authorities need to work with local, state and federal government agencies, industry, private developers, community groups and domestic consumers to make a change. Solutions will vary in scale from household rainwater tanks to precinct-scale stormwater harvesting systems and sewer mining all the way through to recycling wastewater and large-scale stormwater harvesting. We need to address both the supply and demand issues in a way that does not increase the cost of water or level of greenhouse gas emissions.

Are there any specific solutions that could be implemented to meet the water demands from industry?

MC: There are many options that industry can investigate to modify their water supply, use and demands. Each industry and business will have differing water supply demands and uses, requiring an individual review to identify methods of firstly reducing potable water usage, then seeking alternative sources for non-potable uses. Water supply solutions could be at any scale from a small single rainwater tank through to a precinct-wide integrated water management solution such as that proposed for the Doncaster Hill development in Melbourne.

This could result in more cost- and energy-effective solutions for industry if implemented appropriately.

How will our cities ensure water sharing is fair and equitable for the future?

MC: In our modern Australian society, access to fresh, clean water is a basic human right. This principle underpins our current water policy and the actions of governments and water authorities. However, at present, potable water is used in many applications where it is not essential and non-potable sources could be used. As demand grows and supply of potable water is constrained, policy and legislation will evolve to ensure essential potable uses can be supplied and other uses moved to non-potable water sources.

Updates to policy and legislation are crucial in this transition. We will also need to exploit alternative sources of water supply, and integrated water management. The natural alternative is the desalinated sea water, but this is energy intensive so it will only be economically and environmentally viable if the energy source driving the desalination process is renewable.

Clean, fresh water is essential for people and the environment, to maintain our current health and livability standards.

In the UK, water authorities are moving to more natural solutions for water quality treatment and flood mitigation works. The natural flood risk management project in York is a great example of this. By increasing the natural storages, recharging groundwater aquifers and revegetating the waterways and catchments, they can reduce the risk of flooding on the Rivers Ouse and Foss.

Revegetation of the catchments and waterways has many benefits, from improving water quality to reducing flood impacts and reducing the impact of the urban heat island effect. Then there is the benefit of storing carbon to combat the increase in greenhouse gas. Revegetation of rural catchments and urban areas is essential and has a multitude of benefits. Care needs to be taken not to reduce the capacity of waterways in doing this.

How does leadership thinking need to change in order to respond to water security challenges of the future?

MC: We need to understand that this problem requires a long-term plan and long-term investment. By investing in integrated water management solutions and reducing greenhouse gas emissions, we can make our limited supply of clean, fresh water last longer. This will also make our waterways and catchments healthier and more resilient to climate change, flooding and fire. This will come at a cost though, and the price of water may increase to cover the costs associated with the treatment, storage and transfer of water in the future.

Water-sensitive cities require detailed planning, monitoring and implementation. This will ultimately improve the livability of our cities and the health and happiness of residents.

Melanie Collett, Associate Director, AECOM, leads the company’s Water Resources practice. Released for World Water Week, CDP’s infographic report ‘Who’s tackling urban water challenges’, produced in partnership with AECOM and funded by Bloomberg Philanthropies, shows a comprehensive dataset of global water action by cities and companies. Using information gathered from 569 cities and 1432 companies, each reporting their water management activity, it illustrates how global cities and companies are responding to the escalating challenge of climate change and urban population growth.

www.cdp.net/en/research/global-reports/cities-infographic-2017

Image credit: ©stock.adobe.com/au/Butch