Skip to main content

Net Positive Water

Water is a precious resource, and Australians know that better than most. Yet many of us still use drinking water to flush our toilets, cool our buildings, water our gardens, and wash our clothes.

There are other options. Rainwater and stormwater recycling, where projects implement waste water recycling schemes to treat wastewater to a level where it can be used for non-potable demands such as toilets, washing machines, irrigation and cooling towers, is becoming more common in Australia. However it’s not widespread enough, and globally, water harvesting is increasingly used to meet potable water demands as well.

Implementing a wastewater recycling system is a mechanism for creating a closed water loop which can significantly reduce our potable water consumption. A typical residential dwelling has a water balance split of around 70% non-potable demands (washing machines, irrigation, toilets) and 30% potable (drinking, kitchen, shower). In some building types, such as commercial office buildings, this split can be even more heavily weighted to non-potable demands such as toilets and cooling towers.  Yet some upfront planning and investment can create a net positive water cycle, with long-term benefits for owners, occupiers and the environment.

To be water positive, a project needs to meet a few key criteria:

  • Minimise demand as far as possible, through water-efficient appliances/equipment, water-efficient landscape design and through occupant education 
  • Meet demand through on-site water supplies, such as captured precipitation, stormwater harvesting and recycled water and sewerage
  • Only non-potable water used for irrigation
  • Improve the condition of any water leaving the site through chemical-free management and treatment, such that the water leaving the site is in a better condition than the water entering the site and has no negative downstream impacts.

So what are the barriers to implementing a net positive water cycle?

In Australia, the primary challenges we face in achieving a net positive water outcome are related to code, cost and climate. 

CODE: Some jurisdictions have strict rules around water use and water recycling. For example, the Queensland Development Code does not allow the use of treated blackwater as an alternative water source. Based on climate predictions, if water authorities and jurisdictional authorities will not allow alternative water sources to be used for potable demands, then we will have a greater water crisis than we do already. 

COST: Water pricing in Australia is cheap and Government incentives are lacking. Current pricing models are such that, where the cost of a water bill is usually split between connection charges and usage charges, the usage charge is frequently the smallest part of the bill, particularly in residential settings. Therefore not only is water wasted, but payback periods are extended. Systems that can treat wastewater to the standard required for reuse in toilets, washing machines and irrigation, are large pieces of infrastructure that incur a significant amount of capital cost, as well as operational costs for maintenance, testing regimes and energy consumption. Therefore, in most circumstances, there is limited, immediate financial payback for implementing water recycling systems.

CLIMATE: Frequent and long droughts mean we do not always have rainwater or stormwater available for use. Rainwater is a common potable water source outside of major cities, but if there is no rain, there is nothing to drink if rainwater is the only source of potable water. Climate predictions for a lot of Australia are for longer periods of drought, more frequently. Some locations will have increased rainfall, but typically over shorter periods of time, meaning that rainwater tanks will become less reliable, as they fill and overflow, then are rapidly depleted and not refilled for long periods. Our natural water systems such as rivers, creeks and lakes, will behave similarly, putting greater emphasis on alternative water sources to meet both potable and non-potable water needs. 

How do we overcome these barriers?

CODE: There are many national and global areas where reuse of recycled water is allowed (both grey water and black water), and treated water is able to be added to the potable water supply, enabling the most sustainable and optimised water outcomes. Leveraging these built examples can be effective when advocating for change in jurisdictions where there are barriers to water recycling, and when advocating for legislation to incentivize water recycling. Myths that treating stormwater and sewerage could not achieve potable water to World Health Organisation (WHO) standards despite data to the contrary, need to be dispelled.  While change can be slow, advocacy is important to encourage the change to happen and to build on prior success stories. 

COST: Based on current pricing models, in some instances, a positive balance can be achieved, whereby capital and operational costs can be recouped. For example, if a water recycling system is implemented by the water authority on the site, the connection charges can be used to offset the cost of the infrastructure of the recycled water system. This has been a successful model in residential precincts where the density is high enough for piping, pumping and materials to be a relatively lower cost per dwelling. 

In most non-residential cases however, there may be only one or a few connection charges, and the remaining cost is usage. In these instances, based on current pricing models, the capital costs are unfortunately unlikely to be outweighed by operational income. Costs for the operation and maintenance of the recycled water plant and availability of a provider to operate the plant also need to be factored in. Advocacy is required for incentivising water recycling, and adjusting pricing models to have relatively greater costs for water usage. 

Economies of scale come into play with water recycling and treatment. Therefore, implementing water recycling at the scale of a water authority for a region, is far more likely to have a more positive financial balance. Particularly when we take into consideration water shortages due to climate change, and the cost of alternative infrastructure such as desalination plants. Again, advocacy has a vital role to play to support and encourage water positive infrastructure at a regional scale.

CLIMATE: Advocacy to water authorities and jurisdictional authorities to allow alternative water sources to be used for potable demands is again the answer here, to encourage consideration of water as the precious resource that it is, to be used sparingly and reused over and over again. Increasing water recycling and broadening the ways recycled water can be used, is a logical way forward for a water-smart future in this country. 

Case Studies:

Burwood Brickworks Shopping Centre, Wurundjeri Country, Burwood VIC

Burwood Brickworks shopping centre in suburban Melbourne, is the first retail facility in the world to be certified under the Living Building Challenge®(LBC) Petal framework, and in the process of demonstrating full compliance with the LBC. To target the Net Positive Water imperative, Brickworks has implemented a stormwater treatment and reuse system, together with a wastewater recycling system, to meet all non-potable water needs.  Being in a location where connection to the potable water supply is mandatory, the project team for Brickworks connected to the potable supply for drinking purposes, and have advocated to the local water authority for changed legislation that allows potable recycled water.

The water recycling system for non-potable uses involves harvesting sewerage and stormwater from sources across the site and directing it to the blackwater treatment system. Once treated, the recycled water is reticulated within recycled water network pipes, for use in toilet flushing, cooling towers, and irrigation throughout the retail site. Installed in September 2019, the Aquacell system was sized to treat and recycle 60,000L/day of combined blackwater and stormwater, calculated to be the wastewater produced by the building. When tested, the treated water met and exceeded WHO standards, proving its suitability for potable uses.

View the case study here.
Learn more about the project’s water recycling strategy here.

Sustainable Buildings Research Centre (SBRC) – University of Wollongong, Innovation Campus, Dharawal Country, Wollongong NSW

The SBRC, completed in 2013, was Australia’s first Full Living Certified Building (LBC Version 2.1), the 3rd outside of the US and the 24th in the world. To achieve the Water Petal, the first step was to maximise efficiency of the fittings, followed by sourcing recycled water for non potable demands. The majority of the SBRC’s water supply is rainwater harvested from the rooftops of the two SBRC buildings. The rainwater from the 65kL tank is treated without the use of chemicals, a requirement of the LBC, via filtration and ultraviolet sterilization. This treated water is used for showers, amenity hand basins, laboratory hand basins, cleaning purposes, PV wash-down, urinals and toilet-flushing.  The university intends to install a precinct-scale grey water system, therefore the SBRC water distribution is configured to allow toilets and urinals to switch from treated rainwater to grey water, when the precinct system eventuates.

Due to the client’s duty of care as a public institution under local regulations, a public mains potable water connection must be provided for some water demand uses for human consumption or emergency response. These include a drinking water point, a dishwasher, an eye-wash basin for the laboratory and hose reels for fire fighting. These uses have been approved through exemptions.

View the case study here.

The LBC requirements for net positive water are challenging in Australia because of water scarcity and variability, and legislative hurdles in many jurisdictions. However, it is increasingly possible to achieve a significant reduction in demand through efficient design and use of recycled water sources. In areas where recycled water is not yet allowed for potable uses, projects have a role to play in advocacy to encourage change. Many other countries have already made this leap, and only through raising the topic and discussing the possibilities will we start to see these changes in Australia.