How water is shared between the states

The River Murray supports Australia’s largest agricultural region, is home to many unique Australian plants and animals and is the lifeblood for many towns and communities. Water extracted from the River also supports many communities and industries that are not physically located within the Basin.

The climate in Australia is highly variable and conditions differ from year to year and across regions.

Managing the water resources in the Murray-Darling Basin is complex and involves close cooperation and collaboration between the Australian Government, the governments of South Australia, Victoria, New South Wales, Queensland and the Australian Capital Territory (ACT), as well as other state and basin-wide authorities.

Sustainable diversion limits (SDLs) limit how much water can be taken annually for consumptive water use to ensure that there is enough water available to maintain a healthy river system. The River Murray is a highly regulated system with locks, weirs and dams in place to allow careful management and to help meet the needs of towns, communities and food producers.

Water is shared between New South Wales, Victoria and South Australia according to rules set out in the Murray-Darling Basin Agreement (the Agreement), which is part of the Commonwealth Water Act 2007.

This video shows how water from the River Murray is shared and how the Murray-Darling Basin Authority operates the river.

The Murray-Darling Basin Authority operates the River Murray on behalf of Basin governments according to the rules in the Agreement.

Not all water available at the start of the year is able to be shared between States for allocation.

Available water is firstly put towards providing system conveyance and storage losses for the current year and then to the Conveyance Reserve for the following year. System conveyance water is used to “run the river” and to assist with delivering the water for critical human water needs that has been put aside by each state.

Once these needs have been met, the total water that each state will have available to allocate to individual water entitlement holders is determined. This is based on a range of important factors including the volumes of water held in major storages, and the minimum volumes projected to be available over the coming 12 months.

In dry years, each state receives a third share of the available River Murray water.

States may then allocate the water provided to entitlement holders in accordance with state statutory water sharing plans. In South Australia, these are known as water allocation plans.

Water is allocated differently in each state because each has its own management approach to suit the needs of local communities, food producers, industries and the environment. This means that each state has unique water products and different rules and requirements about how and when water is allocated.

The New South Wales water sharing agreements can be found on the Department of Planning, Industry and Environment website and for Victoria on the Northern Victoria Resource Manager website.

Water sharing arrangements within each Basin state must comply with the rules and limits in the Basin Plan. Basin states must show how they are sustainably managing water resources in the Murray-Darling Basin through the preparation and accreditation of Water Resource Plans. South Australia’s three Water Resource Plans are now accredited under the Basin Plan.

To find out more about how water is shared between the states visit the Murray-Darling Basin Authority website.

How water is allocated across South Australia

In total, South Australia has an annual Entitlement of 1,850 GL under the Murray-Darling Basin Agreement.

South Australia does not receive 1,850 GL every year. Whilst access to the full 1,850 GL is available at the start of most water years, it may be reduced when conditions are dry and water availability is limited.

In these years, South Australia receives a third share of the available River Murray resources.

The full Entitlement volume of 1,850 GL includes South Australia’s Dilution and Loss Entitlement of 696 GL. This provides for losses from the South Australian border to Wellington and the dilution component ensures that water of suitable quality for human consumption can be extracted before it flows into Lake Alexandrina.

However, including the 696 GL for dilution and loss purposes does not provide transparency around the components of this water and their purposes, particularly when the other system conveyance volumes are usually not reported in the water availability records of other states. It needs to be remembered that this water is not available for allocation, aside from a small 2 per cent allocation in dry times.

As far back as the 1960s, decisions were made to limit the volume of water that was allocated from the River Murray in South Australia for irrigation. In the 1970s, South Australia required water licences to be converted to volumetric water allocations and a review resulted in a reduction to the internal State allocation limit.

In 1997 a Cap on diversions was implemented across many of the Basin’s river valleys and Sustainable Diversion Limits are now in place across the whole Basin.

River Murray Water Allocation Plan

As with other states, not all of South Australia’s Entitlement is allocated for consumption purposes. This is to ensure that there is enough water for river health.

Once the volume of water available is known, water is allocated to water users in accordance with our state's water allocation plan. South Australia has developed the River Murray Water Allocation Plan in collaboration with the local community and key stakeholders and this outlines the state’s water sharing rules for River Murray water. The River Murray Water Allocation Planwas updated in 2019, to make sure it was compliant with the requirements of the Basin Plan.

A further amendment of the water allocation plan was made in April 2020 to update the private carryover rules. The reference to ‘Class 3’ water access entitlements has also been updated to ‘Class 3 (High Security)’ water access entitlements. This better aligns South Australia’s River Murray irrigation water entitlements with similar products interstate, like New South Wales High Security licences and Victorian High-Reliability shares.

The first water available to South Australia is 696 GL for dilution and loss purposes. This volume is part of the broader system conveyance requirements. It is needed to ‘run the river’ from the South Australian border to Wellington and to ensure that salinity levels do not exceed limits set out in the Basin Plan.

Under extremely dry conditions, the water for dilution and loss may be used to make an initial 2 per cent allocation to Class 3 (High Security) (irrigation) and Class 8 (environmental land management allocations) entitlement holders. This is provided to ensure access for critical human water needs (stock, domestic or industrial) from irrigation systems.

The second priority is water for critical human water needs. Over one million people rely on water from the River Murray for critical human water needs – in metropolitan Adelaide, regional country towns across much of the State and along the River Murray itself.

South Australia requires a maximum of 204 GL for critical human water needs each year. However, in dry times, the initial volume for metropolitan Adelaide from South Australia’s River Murray Entitlement is limited to 100 GL (instead of 150 GL) to allow earlier allocations to irrigators and other water users.

This is because there are a number of water sources to provide water to metropolitan Adelaide, including the local reservoirs, the Adelaide Desalination Plant and water set aside in Basin Storages for critical human water needs. Adelaide’s needs can be met via a range of sources, which has freed up 50 GL for earlier irrigation allocations. This provides up to an 8 per cent increase in allocations when water availability is low, delivering an important boost to irrigators and communities.

Once the requirements for dilution and loss and critical human water needs are met, the next water available is allocated to Class 3 (High Security) (irrigation) and Class 8 (environmental land management allocations) water access entitlements.

Other than in exceptional circumstances, the 8 per cent benefit for irrigators is expected to be maintained in full until 30 June 2024. The commitment will be implemented in a way that has no impact on prices or water security for SA Water customers.

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