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Why does South Australia get water when New South Wales is running out?

Water in the River Murray system is shared between New South Wales, South Australia and Victoria because the River Murray runs along the border of New South Wales and Victoria, and then into South Australia. Most years, South Australia gets a fixed amount of water. New South Wales and Victoria receive their share of the available water according to the rules of the Murray–Darling Basin Agreement. South Australia then receives a fixed amount of water called its entitlement that must be supplied 50:50 by New South Wales and Victoria from their shares. This means that New South Wales and Victoria receive much more water than South Australia in a wet year and sometimes less in a dry year, whereas South Australia’s water share usually remains the same.

The River Murray is Adelaide’s main water source. If not enough water reached South Australia from the Basin river system, South Australian communities, businesses and the environment would struggle to survive.

This page explains

  • Why water must continue to flow to South Australia
  • Why South Australian farmers receive water when farmers in parts of other states may not.

The River Murray supplies Adelaide with water

The River Murray flows through the eastern part of South Australia. It is Adelaide’s main water source, sometimes supplying more than 80% of the city’s water. Adelaide’s water supply is supplemented by rain, groundwater and water from the Adelaide Desalination Plant, but these sources can be less reliable, more expensive, or worse for the environment than drawing water from the River Murray. To make sure demand for water can be met, South Australia receives 1,850 gigalitres of water from the River Murray each ‘water year’ (in this case, 1 June to 31 May), except in years where there is very little water available.

Water sharing rules give South Australia a fixed amount of water most years

The rules for sharing water between the states date back to 1914 when the River Murray Waters Agreement was first signed. This Agreement gives South Australia a fixed amount of water (1,850 gigalitres) from the River Murray system every year, except when there is very little water available (for example, after several dry years in a row). This 1,850 gigalitres includes water to keep the river flowing and water to cover some conveyance losses. Victoria and New South Wales both generally receive half of the remaining available water in storage, rather than a set volume. This means that even though South Australia usually receives a smaller share of water than either New South Wales or Victoria, it can depend on a more consistent amount of water from year to year. The result of this is that in some dry years, and especially when there have been several dry years in a row, South Australia is more likely to have water to distribute to its entitlement holders than New South Wales. However, in years where water availability is extremely low, South Australia may get less than its usual 1,850 gigalitres of water, and as a result will have less water to distribute to entitlement holders.

South Australia only gets extra water in a wet year, when there is too much water and it can’t be stored in dams along the River Murray, so it flows downstream.

Not all of New South Wales’ water comes from the River Murray

While most of inland New South Wales falls within the Murray–Darling Basin, not all of its water comes from the River Murray. Water for irrigation also comes from other major rivers such as the Darling, Barwon and Murrumbidgee.

The amount of water farmers get is based on the water available in the catchment they are in. Water availability in the Basin depends on how rain and hot weather impact the rivers and storages. In the northern part of the Basin it is much drier and rainfall is less reliable. Entitlement holders in these areas can’t rely on receiving their whole allocation of water from year to year.

In South Australia, the vast majority of water comes from the River Murray. Because South Australia usually receives a fixed amount of water from the Murray, and because it has less entitlement holders than in other states, South Australian entitlement holders are more likely to receive their whole allocation each year.

The River Murray is a resource for communities, plants and animals

As well as farmers, there are many other people, plants and animals that rely on water flowing through the River Murray in South Australia. It sustains towns and communities, is needed to maintain sacred First Nations’ sites, rejuvenates wetlands and supports the breeding patterns of birds, fish and other aquatic wildlife in the Lower Lakes and Coorong — unique ecosystems that are home to many endangered species.

Questions you might have

“Why doesn’t New South Wales walk away from the Basin Plan?”

Withdrawing from the Basin Plan would not increase New South Wales’ share of water from the River Murray system. The rules for sharing the water are laid out in the Murray–Darling Basin Agreement, not the Plan.

One of the main aims of the Basin Plan is to recover water for the environment. Because of this, some people think that New South Wales should ‘walk away’ from the Plan so that its irrigators can continue to use water that would otherwise go towards improving the health of the rivers. The Basin Plan is Commonwealth law and, even if New South Wales was to withdraw, the Basin Plan would remain in place and water for the environment would still exist.

Besides this, walking away from the Basin Plan would be a short-term solution that would cause serious damage to the environment and ultimately increase problems like salinity and acidic soils. Water quality would decrease, and there would be less high-quality water available for everyone, including irrigation farmers.

“Why can’t Adelaide get all of its water from desalination?”

Adelaide's desalination plant can produce a maximum of 100 gigalitres of water a year, which is about half of Adelaide's drinking water. It usually only produces about 8 gigalitres of drinkable water because desalination is extremely expensive and uses a huge amount of energy. In 2019–2020 about 40 gigalitres was expected to be produced and in 2020-2021 the amount of water produced may increase to 60 gigalitres as part of a drought-relief program. The amount the desalination plant produces may continue to increase in the future.

However, increasing the amount of water produced by desalination would not mean that South Australia would no longer rely on the River Murray. Irrigation farmers, people living in rural communities and a portion of Adelaide’s population would still require water from the river. Water also needs to flow out of the Murray Mouth to release salty water from the system and refresh the Lower Lakes, whose plants and animals need freshwater to survive.

“Why is water allowed to flow into the Lower Lakes and sea instead of being used for farmers?”

The Lower Lakes have historically been mostly freshwater. This has been proven by analysing fossils and from a range of other scientific evidence and historic records outlined in the Lower Lakes Independent Science Review. The Lower Lakes and Coorong are Ramsar-listed sites, meaning they have been recognised as internationally significant and must be protected because they provide important breeding grounds for fish, native and migratory birds, and other wildlife.

Allowing the Lower Lakes to fill with seawater would not benefit them. Instead, it would drastically alter delicate ecosystems, and many animals would die. It would also negatively impact local agriculture and would not provide additional water to entitlement holders.

Water also needs to exit the Basin rivers via the Murray Mouth to maintain water quality. Excess salinity builds up in the water during its journey from headwater catchments to South Australia. If water did not flow into the sea, water in the Lower Murray would eventually become too salty to be used for drinking or growing crops.

The water that flows through the Murray Mouth also has benefits upstream. This water, as it makes its way down the River Murray, provides water to important wetlands, creating a habitat for native species and providing benefits to river communities. The water then returns to the river system, often repeating the process through other wetlands, until in reaches the mouth. This means the water leaving the mouth benefits the entire river system.  

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Updated: 30 Sep 2020