Water sources

Water is vital for life, and plays a critical role in the health of our communities, economy and ecosystems. Australia is the driest inhabited continent on Earth, with a mean annual rainfall of 457 millimetres (mm) (1900–2020). Our climate is highly variable, both across the country and from year to year. The frequency and intensity of extreme events, such as droughts and floods, are important characteristics of the Australian climate.

In many parts of Australia, our highly variable rainfall has a significant impact on the availability of water resources (Gill 2011). Australia’s streamflow is the third most variable in the world; its variability is double that of most other countries, based on an analysis of streamflow data for 1,221 rivers from 36 countries across the globe (McMahon et al. 2007b, McMahon et al. 2007a, McMahon et al. 2007c). This, coupled with the increasing demand for water caused by population and economic growth, presents unique challenges for the management of Australia’s water systems and supplies.

Lower rainfall and streamflows since 2016 have resulted in pressure on Australia’s water storages and record low allocations to water licence holders. The limited availability of surface water has also resulted in increased water market activity and unprecedented prices being paid for water in the Murray–Darling Basin (see Water markets), where prices exceeded $700 per megalitre (ML) in December 2019. Although most of the water trades occur in the southern Murray–Darling Basin, there are also sizeable water markets in other areas, including Queensland (outside the Basin), Tasmania, and south-west and north-east Western Australia. Between 2018–19 and 2019–20, the volume of trade in Tasmania increased by 53%. Over the same period, the price paid in the Harvey trading zone in Western Australia increased by 40% (BOM 2020c, BOM 2021a).

Low surface-water availability saw an increased reliance on desalination to supply water to major urban centres; all capital cities and regions that have desalination plants (i.e. Adelaide, Melbourne, Perth, south-east Queensland and Sydney) reported a significant increase in production. Groundwater was an increasingly important source of water for both urban and rural users, and many aquifers experienced limited recharge and recovery and did not return to pre–millennium drought levels.

Rainfall

From July 2016 to June 2017, Australia experienced above-average rainfall and higher-than-average streamflows, with largely wet conditions for the first 9 months and a dry period from April to June (Figure 1a).

However, from July 2017 to June 2019, much of Australia saw a return to drought conditions, with widespread rainfall deficiencies accompanied by high maximum and minimum temperatures (Figures 1b, 1c and 1d). Australia’s mean rainfall for July 2017 to June 2018 was 4% below the long-term mean. Streamflows in most rivers across south-eastern Australia were lower than average, and many rivers recorded their lowest flows on record, particularly in the northern Murray–Darling Basin.

The delayed monsoon period over the 2017–19 financial years contributed to below-average wet-season rainfall in northern Australia. This resulted in absence of the normal filling and spilling of storages in northern Australia. In 2020, heavy rainfall associated with ex-tropical cyclone Esther brought some relief to the drought conditions across the base of the Top End and the northern half of the Kimberley.

The very-much-below-average rainfall continued throughout July–December 2019 due to a positive phase of the Indian Ocean Dipole, one of the strongest on record, that influenced Australia’s climate during this period. There was some rainfall relief during the early part of 2020 as tropical moisture associated with warmer-than-average sea surface temperatures off the north-west coast of Australia moved across the continent and combined with southern cold fronts to produce high rainfall across the eastern seaboard. Heavy rainfall associated with a coastal trough in early February 2021 contributed to well-above-average rainfall in coastal New South Wales, Queensland and Victorian areas, resulting in increases in storage volumes for the first time in 3 years.

Two heavy rainfall events across the upper Diamantina and Georgina river catchments from late January to March 2019 generated notable run-off into the Kati Thandi–Lake Eyre Basin. Late 2020 saw the climatic conditions change with the arrival of La Niña conditions, and dam levels rose to healthier levels. However, the rain created sludge-like water quality in river systems affected by the 2019–20 summer fires.

Despite these rainfall events, the area-averaged rainfall across Australia for the 2019–20 financial year was 347 mm, 24% less than the long-term mean of 457 mm. Over the 2018–20 calendar years, Australia experienced its driest 24-month period on record.

Although 2020 saw many coastal areas around Australia recovering from the drought conditions of the previous years, the Murray–Darling Basin continued to experience rainfall deficiencies (Figure 2).

Surface water

Australia’s surface-water resources include our rivers, dams and reservoirs.

Drainage divisions and rivers

The Australian continent is divided into drainage divisions, which are subdivided into water regions and then into river basins. The drainage divisions depict where water flows across the continent and identify the major hydrological basins. There are 123 National Catchment Boundaries Level 1 drainage divisions, as defined by the Australian Water Resources Assessment 2012 (BOM (2013); Figure 3 and Table 1).

In the 2016 state of the environment report, the drainage divisions were used as the basis for assessments; in this report, the finer unit of river catchments within each drainage division is used.

Dams and reservoirs

Australia’s high variation in rainfall and streamflow, as well as high temperatures, has meant that large reservoirs have been built to ensure reliable supply (McMahon et al. 2007b, McMahon et al. 2007a, McMahon et al. 2007c); most rivers suitable for the construction of storages have already been dammed. Australia has more than 500 major surface-water storages (a major storage is considered to be one with a total storage capacity of 1 gigalitre (GL) or more), several thousand small storages and more than 2 million farm dams. The total accessible storage capacity is about 81,000 GL (BOM 2018c), equivalent to a national per-person surface-water storage capacity of about 3.25 ML. This is relatively high compared with many other countries; for example, India has 0.185 ML per person, China has 0.57 ML, South Africa has 0.75 ML, and the United States has 2.26 ML (AQUASTAT 2017).

After the end of the millennium drought (mid-2010), the combined accessible storage volume across Australia climbed to around 80% in late 2011 and remained at or above this figure until the end of 2012 (Figure 4). The stored volume then slowly dropped to below 50% of capacity in March 2016, where it stayed until June 2016. It rose to 70% in early 2017 and again in spring 2017 due to the wet weather throughout much of Australia during 2016–17. However, with the prevailing dry conditions across Australia after this time – and continued diversions from storages – the accessible storage continued to decrease, falling to around 45% of capacity by January 2020, the lowest level in more than 10 years. The combined accessible storage volume recovered to some degree after February 2020 following higher rainfall across south-eastern Australia and reached 52% by the end of 2020.

Individual storages experienced considerably lower levels, especially in the northern Murray–Darling Basin and in northern Australia (Figure 5). Although the storages in these regions experienced some recovery, they did not reach full capacity – especially in the northern Murray–Darling Basin, where the large storages were less than half full for the period from 2018 to 2020.

Groundwater

Groundwater plays a significant role in Australia as a supply for drinking water, industry, farming and other primary industries in the many regions where groundwater is the only reliable water source. It also plays a crucial role in the Australian landscape for groundwater-dependent ecosystems. Groundwater is home to freshwater and underground species, many of which are yet to be explored (see the Biodiversity chapter).

Iconic groundwater resources in Australia include the Great Artesian Basin, which covers one-fifth of the continent; the major alluvial aquifers of the Murray–Darling Basin, which support Australia’s major food bowl; and the Perth Basin, which supplies much of Perth’s water demands (Figure 6). Many other crucial groundwater resources occur in other areas and are important for sustaining communities, agriculture and the Australian economy.

Declining groundwater levels

The return to drought conditions since 2016 and the resulting decrease in surface-water availability have seen an increase in the dependency on groundwater. Many aquifers have experienced limited recharge and recovery, and have not returned to pre–millennium drought levels (BOM 2021c).

Other threats to groundwater include:

• reductions in rain events associated with climate change
• overextraction
• contamination
• saltwater or seawater intrusion
• mining and coal-seam gas extraction.

The decrease in groundwater levels has adversely affected groundwater-dependent ecosystems. Examples of ecosystems in Australia that depend entirely on groundwater include the Great Artesian Basin spring ecosystems, the Pilbara spring ecosystems, and the permanent lakes and wetlands of the Swan Coastal Plain (Harrington & Cook 2014).

The sustainability of groundwater use is subject to the pressures of climatic conditions and extractions. Recharge rates are typically very small compared with the volumes in the aquifer. Over time, water from rain and rivers travels through the ground and collects in underground rock fractures or between grains of sediment. The layering and structure of aquifers and aquitards make up the groundwater system and dictate how water flows below the ground, and sustains rivers, wetlands and vegetation at the surface.

From 2015 to 2020, the trend in upper aquifer groundwater levels ranged from stable (41%) to declining (30%) and rising (29%) (see Figure 7) (BOM 2021c). Stable or rising groundwater areas are those that have experienced wetter conditions despite the national rainfall being very much below average, whereas declining areas are where extraction has exceeded natural recharge. Similarly, most bores in the middle and lower aquifers, where most extraction occurs, had below-average groundwater levels (56% and 54%, respectively), with generally stable or declining trends.

In south-east mainland Australia, including the Murray–Darling Basin and south-east Queensland, most bores had below-average groundwater levels and stable or declining trends. Areas of high groundwater extraction (e.g. the alluvial aquifers in the north-east of the Murray–Darling Basin, such as the Namoi) were particularly affected by high levels of extraction. The low groundwater levels in the Murray–Darling Basin and south-east Queensland reflect limited aquifer recharge due to the low rainfall experienced across the region over the previous 3 years, coupled with an increase in the volume of allocated groundwater that was taken. Similarly, bores in the Darwin and Daly–Roper water control districts in the Northern Territory had declining trends because the normal increase in groundwater levels during the wet season did not occur, as a result of 2 poor wet-season rainfalls. The lack of wet-season recharge was exacerbated by increased groundwater extractions, especially during 2019.

In south-west Western Australia, groundwater levels have generally been in decline for the past 40 years due to decreasing rainfall (BOM 2018c), coupled with increasing groundwater demand. Measures to reduce and redistribute groundwater extraction have been undertaken to slow the rate of groundwater decline, and groundwater trends in the previous 5 years have been mostly stable.

Defining ‘sustainable’ groundwater levels is difficult because adequate groundwater models are lacking (CSIRO 2009). In the absence of quantifiable information, the Western Australian Water Corporation has developed ways to manage groundwater sustainably and reduce the amount of groundwater being used. These include expanding the number of aquifers from which groundwater is taken, replenishing deep aquifers by managed aquifer recharge, and taking water from coastal surface waters.

Groundwater levels measured from bores are one of the few direct measurements available to understand changing groundwater conditions. Groundwater typically responds slowly to direct climatic variability, especially in comparison with surface water. Therefore, the 5-year trend from 2015 to 2020 is used to assess the changes to groundwater levels. The groundwater level trend analysis presented here uses a simplified representation of the 3-dimensional groundwater systems across Australia, aggregating them into upper, middle and lower groups, as presented in the Bureau of Meteorology’s Australian Groundwater Insight.

Great Artesian Basin

The Great Artesian Basin is Australia’s largest groundwater basin and is one of the largest underground freshwater resources in the world. The Basin spans almost 1.7 million square kilometres (more than one-fifth of the Australian continent) and has a storage capacity of 64,900 million megalitres. It connects with the Murray–Darling Basin and the Lake Eyre Basin, and lies beneath parts of New South Wales, the Northern Territory, Queensland and South Australia (DAWE 2021c) (Figure 11).

Effective management is important to ensure conservation of this important water source. The Great Artesian Basin Strategic Management Plan was developed by the Australian, New South Wales, Northern Territory, Queensland and South Australian governments and published in 2020. The plan spans 15 years (ending 2034) and is to be reviewed every 5 years. It was developed in consultation with the Great Artesian Basin Coordinating Committee and stakeholders.

The plan provides a framework for governments, Indigenous people, water users and other stakeholders to achieve economic, environmental, cultural and social outcomes for the Great Artesian Basin and its users. Basin governments, and community and industry representatives agreed to 7 guiding principles to achieve these outcomes:

• coordinated governance
• a healthy resource
• Aboriginal and Torres Strait Islander values, cultural heritage and other community values
• secure and managed access
• judicious use of groundwater
• information, knowledge and understanding for management
• communication and education.

A Great Artesian Basin Stakeholder Advisory Committee (GABSAC) is planned to be established in the near future under the Great Artesian Basin Heads of Agreement between the Australian Government and Basin state and territory governments. The GABSAC is designed to:

• advise on whole-of-Basin policies and initiatives
• present the views of industry, communities and other stakeholders.

As the plan has only been in operation for 1 year and the GABSAC has not yet been appointed, assessment of its effectiveness or impact for the Basin is not possible.

Other water sources

Urban centres across Australia face the challenges of growing populations with increased water needs and often a declining reliability of existing water resources. This can arise from ageing of assets, sedimentation of storages, changes in climate and deterioration in water quality.

Australia’s streamflow variability has increasingly led to the need to develop other water sources. This pressure is likely to increase with climate change. Climate-resilient sources such as seawater desalination and water recycling have been introduced to improve the security of urban water supply, especially during dry periods (Figure 12).

Desalination

Australia has around 270 desalination plants, mostly small scale, to desalinate marine and brackish water for various uses. The total desalination capacity across Australia is about 880 GL of water per year. The 5 largest urban areas in Australia have a total seawater desalination capacity of 534 GL per year (BOM 2021c).

Perth has relied on desalination to provide nearly half its water supply for some years because of a steady decline in streamflows to Perth water storages over the past 4 decades (BOM 2021c). The volume of water sourced from desalination by other capital cities has previously been small, with total desalinated water usually making up less than 10% of the total for these cities (Table 2). Although the volumes of desalinated water that were produced before 2019 were low (except for Perth), production increased significantly during the latter half of 2019 (Table 2).

In recent years, low surface-water availability, particularly in the latter half of 2019, saw urban utilities opting to reduce pressure on their surface-water resources and increase their reliance on desalinated water supply to meet urban demand, with desalinated water making up 4% of total water supply. Sydney, in particular, increased desalination; and by December 2019, when Level 2 water restrictions were introduced, its desalination plant was operating at full capacity and providing 7% of Sydney’s water supply. Melbourne and Adelaide also significantly increased the percentage of water supplied from their desalination plants.

Recycled water

Water recycling involves treating wastewater to a suitable standard so that it can be used for beneficial uses such as nonpotable domestic uses, irrigation of public places, agricultural irrigation, industrial uses and groundwater recharge.

Water recycling is attractive in situations where available sources cannot meet the growing demand. It provides a reliable supply, because water is consistently available throughout the year as it is produced from wastewater flow from the cities. Water recycling can also improve environmental outcomes by reducing the amount of treated wastewater discharged to the receiving waters and reducing the draw on other water sources. Australia’s 5 largest urban areas have significant recycled water use, and this is increasing, especially in Melbourne and Adelaide (Figure 13) (BOM 2021c).

Of note is Perth’s Groundwater Replenishment Scheme, which started in late 2017. The scheme treats wastewater to drinking water standards and charges it back into the groundwater store for future use. Stage 1 is fully operational, and construction of stage 2 is under way. The construction of 4 recharge and 4 monitoring bores across 2 recharge locations (Wanneroo and Neerabup), along with a 13 km recharge pipeline connecting the water recycling plant with the bores, has been completed (Water Corporation 2019). It is expected that 20% of Perth’s water supply will be supplied from groundwater replenishment by 2060 (Water Corporation 2009). Managed aquifer recharge, including where it can take place and what the water can be used for, is regulated by the Department of Water and Environmental Regulation through the issuing of water and environmental licences and permits. As part of the Groundwater Replenishment Trial conducted by the Water Corporation in Australia (2009–12), extensive community and stakeholder engagement was undertaken to build acceptance and support for groundwater replenishment as a future water source (Bettini & Head 2016).