The Goyder Institute's Managed Aquifer Recharge and Stormwater Use Options (MARSUO) project has been the first to lay down a serious and rigorous body of evidence in support of harvesting stormwater to augment urban water supplies. It has transparently examined the social, technical, economic and environmental facets.

In Adelaide there is strong public support for stormwater for drinking and non-potable supplies and it has been in use by innovative local councils for 20 years, for public open space irrigation. Stormwater presents opportunities for securing city water supplies at much lower unit costs than desalination; indeed, had this project been completed siz years ealier, several states might have significantly reduced major capital outlays.

Owing to the mainly impervious nature of urban catchments, stormwater yields are more reliable and less drought-prone than rural runoff. The challenge of storage can be met by using surface reservoirs or aquifers, sometimes in combination. Urban stormwater quality is similar to that from open catchments that source drinking water for a number of Australian cities. The treatment and distribution technologies required are little different than those for conventional sources.

Despite the intuitive appeal of stormwater harvesting, the science and technology are not trivial, especially when aquifers are involved. This effectively places lower limits on project size to achieve economic sustainability. As is the case with any field of endeavour, a body of empirical practice rules has to be generated to ensure practical success. This project has made a good start in that direction.

The political realities of creating innovative systems have to be addressed too, as agencies and water businesses weigh up the threats and opportunities which are opened up, and the different relationships that have to be managed. Regulators need to create an environment which encourages innovation and fosters a market driven climate for all the players.

For many potential stormwater/MAR projects around Australia, there is insufficient value ascribed to environmental benefits, so more attention is needed in that respect.

Although the evidence from this project suggests that stormwater harvesting can be competitive in overall cost terms, every project is unique and a rational evaluation of costs and benefits is needed.

The MARSUO research project was a 3.5 year project that ran from November 2010 to May 2014. It evaluated in depth the quality of stormwater generated in the City of Salisbury, the treatment requirements and risk management measures necessary to assure safe water quality for public open space irrigation, third pipe reticulation to homes and for potential drinking water supplies. It also evaluated and compared the economics of these options for a case study at Parafield in Salisbury, South Australia, accounting for basic assessments of environmental and social impacts. Focus groups and two web surveys were conducted to evaluate public acceptance of the different potential uses of stormwater. An evaluation of biofilm in pipes of different materials was undertaken for mains water and stormwater to assess the likelihood of water quality changes and potential impacts on infrastructure maintenance. Studies of satellite sites in Australia and overseas were undertaken for comparative purposes, analysing stormwater quality and treatment requirements for drinking water use in relation to the Salisbury results.

These research studies were initiated in order to support the South Australian Government water security plan Water For Good that was announced in 2009. One of the key aims was for up to 60GL/yr of stormwater to be harvested in Adelaide, and up to 15 GL/yr in regional South Australia, by 2050. Additionally, these studies also became an integral input into the National Water Reform Initiative to assess the suitability of all forms of water for water supply, and to determine the economic benefits and public acceptance of diversification of urban water supplies. The overall premise was to identify and increase the range of efficient water supply sources whilst also reducing the environmental impacts of stormwater as Australian cities grow and urban areas consolidate. All of the approaches and principles that were applied were compliant with the Australian Guidelines for Water Recycling in the National Water Quality Management Strategy. Water quality was monitored at a number of sites to inform a risk assessment which then led to the development of a risk management plan.

From a national perspective the MARSUO project demonstrates the utility of stormwater for a wide range of future uses.

• It suggests that drinking water uses can be considered in addition to public open space and industrial use as well as third pipe residential supplies, in line with the NWI principle that all sources of water should be considered for future drinking water supplies
• Local data are needed, however an example shows that treatment costs to augment drinking water supplies with stormwater can be cheaper than the costs of establishing separate non-potable water distribution systems, and are similar to treatment costs to produce drinking water sourced from reservoirs in open catchments
• Aquifer storage (even in brackish aquifers) has value in increasing the capturable volume and through its potential for water treatment, and alone or in combination with reservoirs, reducing the unit costs of supply
• In a drying climate, the yields of urban catchments will diminish only marginally in comparison with decline in yields in rural catchments, and stormwater would provide a more dependable supplementary supply if systems were connected
• As drivers for sectors of the water industry can be quite different and the best commercial stormwater use options for any utility are not necessarily the optimal use for the city as a whole, and may therefore invoke loss of opportunity benefits unless such benefits are identified
• Policies are necessary to align commercial opportunities with best and most efficient use of the resource

Jurisdictions that have previously ruled out potential sources of water for cities without consideration of their merits should be encouraged to reconsider so as to fully implement the principles of the National Water Reform Agenda agreed to by the Council of Australian Governments.

Capitalising on the water supply opportunities for stormwater use options may require a more unified form of water governance than exists in most States, which recognises the integration of existing stormwater drainage and mains distribution infrastructure with different ownership and different established financial arrangements.

Water sensitive urban design, as encouraged in many jurisdictions, when implemented will improve the quality, increase the harvestable volume of stormwater and thereby advance opportunities for drinking water supplies. Urban designers should be free to consider the full palette of stormwater use options.

The MARSUO project shows that the technical and water quality/safety aspects are manageable using established processes under the National Water Quality Management Strategy, and the next step is to build processes that enable timely financial integration so that the highest valued projects are supported.