This page explains how water in the River Murray system is shared between New South Wales, Victoria and South Australia.
Water in the River Murray is shared between three states
Sharing the water
The River Murray runs along the border of New South Wales and Victoria and then into South Australia. All three states rely on a certain amount of water from the river. The MDBA is responsible for calculating each state’s share of water from this part of the Basin river system, because special rules apply to how this water is shared between states before it can be allocated to farmers and other water users. These rules are outlined in the Murray–Darling Basin Agreement.
To understand more about how water is allocated, visit:
The MDBA calculates each state's share of water from the River Murray
The way water in the River Murray is shared between states was first agreed in 1914 as part of the River Murray Waters Agreement. The current water sharing arrangements were agreed in 1989 and formalised in 2007, in the Water Act (2007). They are set out in the Murray–Darling Basin Agreement which comprises Schedule 1 to the Water Act 2007 (Cth) (the Agreement).
The MDBA is responsible for sharing water according to this Agreement. It acts as an independent body to make sure each state gets the water it is entitled to from the major River Murray storages (the Hume and Dartmouth Dams and Lake Victoria), and in some instances, water from the Menindee Lakes.
Water is not simply divided into three even parts. Victoria and New South Wales each receive:
- 50% of water flowing into the Hume Dam
- 50% of water flowing in the Kiewa River
- 50% of water flowing into the Dartmouth Dam
- 50% of water in the Menindee Lakes when they contain more than 640 gigalitres of water, at which point the MDBA has access to the lakes. When the amount of water falls below 480 gigalitres, only NSW receives water from them until they next reach 640 gigalitres.
South Australia receives a maximum volume (currently 1850 gigalitres) which it can rely on in most years, except when there has been very low rainfall. Victoria and New South Wales each provide half of South Australia’s share from the water they have available.
Calculating and forecasting water availability
The MDBA provides fortnightly updates on how much water in the River Murray system is available to each state.
To calculate this amount, the MDBA first works out how much water has to be kept in reserve for:
It also tracks:
- the total amount of water in the system including stored and 'in transit' volumes
- water usage in New South Wales and Victoria
- water supplied to South Australia.
Tracking water helps the MDBA regularly assess how much water is likely to be in the system in the coming months.
The MDBA uses computer modelling with input data that describes the current system status and forecasts based on statistics of inflow and state advice on usage when calculating water availability. It uses data for the driest possible scenario to work out the minimum amount of water available to each state across the year.
The total amount a state is given each month includes consideration of water that will flow into the system, losses, and the amount of water that they currently each hold in major storages.
States then use this advice to help them determine water allocations for entitlement holders along the Murray.
More water accounting principles and rules are detailed in the Agreement.
States own some water in the River Murray
Not all the water in the River Murray system is shared between the three states. Water flows into the Murray from tributaries in both New South Wales and Victoria. Water flowing into the Murray from rivers downstream of Albury, such as the Murrumbidgee and the Goulburn, is owned by the state the water flows through.
On average, Victorian tributaries deliver more than double the amount of water to the River Murray than New South Wales tributaries (about 3,317 gigalitres compared to 1,543 gigalitres a year). As a result of this, Victoria usually has more water available in the Murray, compared to New South Wales.
The map below shows who owns the water in different rivers.
The Murray–Darling Basin Agreement sets out how water is shared
A water sharing agreement was first signed in 1914 when New South Wales, South Australia and Victoria came together to make sure water in the River Murray was managed fairly and to leave South Australia with enough water. The Agreement has been updated a few times since then.
The Agreement sets out rules and plans for dividing the water in the River Murray to support a reliable supply of water for communities and environments along the River Murray across the three states.
What is now the Murray–Darling Basin Agreement has been updated several times, most recently in 2018 to implement the Basin Salinity Management 2030 strategy, and adjustments have been made to the amount of water South Australia receives from New South Wales and Victoria.
The Basin states and the Australian Government have all signed the Agreement, and each state contributes funding for managing the River Murray based on its level of water use and the benefits it receives from the collective management of this important resource.
