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Common water management terms

Definitions of water management terms frequently used by the MDBA.


The amount of water a water entitlement holder receives in a given year.

An allocation is different to an entitlement. An allocation is the proportion of the entitlement held that can be made available reflecting how much water is available in the system. The percentage depends on the amount of rainfall, inflows into storages, and how much water is already stored. Allocations can increase throughout the year in response to changes in the system. Allocations can be traded, meaning an entitlement holder can sell their water in one year, but still have an ongoing share of water for the following year.

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Basin state

A state (or territory) with an area of the Murray–Darling Basin within its borders. Usually, the term is used to mean the governments of those states.

The Basin state governments are New South Wales, Queensland, South Australia, Victoria and the Australian Capital Territory.

Bulk water share

The amount of water in the River Murray system that can go to each state based on the Murray–Darling Basin Agreement.

This amount is calculated by the MDBA, as per the rules of the Agreement. The states then calculate how much water they can allocate to individual water entitlement holders.

Also known as: bulk share

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An unused water allocation (or part of an allocation) that the water entitlement holder saves for the next water year.

Carryover gives a water entitlement holder a right to a share of space in storage dams and the right retain any unused water for use in a later year.

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A catchment is an area of land, usually surrounded by hills or mountains, where water naturally collects. Gravity causes all rain, melting snow and other water in the catchment to run downhill where it flows into creeks, rivers, lakes or oceans.

The Murray–Darling Basin is divided into 22 catchments.

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Delivery of water

Physically getting water to the users who have ordered it. This includes providing water to state storages (in some cases), individual irrigators and environmental water holders. This involves managing the flows and connections of water in the river system. This is done jointly by the MDBA, the states and state partners such as Irrigation Infrastructure Operators, by operating infrastructure in the river system.

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Sustainable diversion limit

The limit on how much water can be used by Basin towns, communities, farmers and industriesover the long-term, while leaving enough water in the river system to sustain natural ecosystems.

Sustainable diversion limits are set at a catchment level so that there is enough water for all users, including the environment.

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Water entitlement

The ongoing right to a share of the available water in the river system up to a maximum amount.

An entitlement is not the same as an allocation. For example, a farmer might own an entitlement that gives them the right to a maximum of 100 megalitres of water each year. However, they are not guaranteed to receive the entire 100 megalitres of water in a particular year. The amount they get depends on overall water availability. For example, in a dry year, the farmer might only receive a 50% allocation of their entitlement, or 50 megalitres.

Entitlements can be bought or sold, but once sold, the seller loses the right to a regular share of the water

Also known as: water right, water license

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Water entitlement holder

Water users who own a water entitlement. These can be individuals, communities, farms, businesses, or governments (environmental water holders).

Also known as: license holder.

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Water trading

Buying and selling water entitlements and allocations.

When someone buys or sells an entitlement, this is a permanent purchase or sale of the right to water. When someone buys or sells an allocation, this is the purchase or sale of  the right to some or all of the water that has been allocated to a water user.

Anyone holding water rights can trade entitlements and allocations freely, except where there are physical constraints (such as geography or lack of connections to the system that are managed by trading rules) or water supply considerations.

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Water flowing into a storage (reservoir or lake) or river system. Inflows can be natural, resulting from rain or snow over catchments that runs off into tributary creeks and rivers; or regulated – where releases from storages or other structures (such as pipes or power stations) located upstream or outside of the system or storage have some influence or control over the arriving flow. Inflows are measured by gauges deployed just upstream of their junction point or connection into the system or storage.

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The water under the Earth’s surface.

Groundwater is found in geological basins and spaces between cracks in soil and rock. These are called aquifers or groundwater systems. Groundwater can flow into rivers and wetlands through channels, springs or by seeping from rock. Groundwater often needs to be recharged by rainfall. In some systems this can take days, while in others this can take months or years. 

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Critical human water needs

The minimum amount of water required to meet basic human needs.

As well as water for drinking and livestock, critical human water needs includes water for vital social or economic requirements, such as water for significant local industries or community uses.

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Return flows

Water that returns to the river from floodplain areas and wetlands.

Return flows happen in two main ways:

  • surface water return flows, when water trickles back into the river through channels, drains and creeks
  • groundwater return flows, when water seeps into the ground, pushing groundwater into the river.

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Updated: 30 Sep 2020