Water sharing plans developed by the NSW Office of Water in consultation with the community determine how much water can be extracted over the long-term and how much needs to be set aside for the environment.
On a yearly basis, how much water can be extracted varies according to rainfall, inflows to the storages, evaporation and the efficiency of water delivery infrastructure.
At the start of each water year on 1 July, the Office of Water makes Available Water Determinations (AWDs), more commonly referred to as 'water allocations', which specify how much of their water entitlement licence holders can extract from a river or aquifer over the course of that year.
If the annual determination is less than 100 per cent, the Office of Water will review water availability on a regular basis and, when possible, announce revised water allocations.
Allocation announcements are made in the media.
Information about water allocations/available water determinations can be accessed in a number of ways:
Indicative water availability outlook
To assist with forward planning, the NSW Office of Water prepares an indicative water availability outlook from time to time for some water sources, particularly in the southern basin where the rules and sharing arrangements are more complex.
How water is allocated
Water is allocated in accordance with the rules of the relevant water sharing plan and the available water. When determining how much water will be allocated to water users, there are number of considerations, including:
- How much water is in storage and how much of that is carried over as unused water from the previous year, including undelivered inter-state trades, where applicable, and
- How much water is expected to flow into the dams and lakes from natural inflows over the remainder of the water year, i.e. until 30 June.
In making the water resource assessment, the lowest recorded inflow sequence is used so that the Office of Water does not allocate water that is not very likely to flow into the storages. Not all inflows contribute to increasing allocations. For more information on how water was allocated in the Murrumbidgee Valley in 2012, download the factsheet below.
Supplementary water, formerly known as off-allocation water, is effectively surplus flow that cannot be conserved. When storm events result in flows that cannot be controlled (regulated) in storage structures such as dams or weirs for future use, and the water is not needed to meet current demands or commitments, then it is considered surplus to requirements. Regulated rivers become unregulated for a period of time.
As soon as these conditions are identified, a period of Supplementary Access is announced and details of the subject river reaches and time periods are published. Licence holders generally can choose to pump water during these periods as usual. However, those people with Supplementary Water Access Licences can only pump water against these licences during these announced periods. Those holding General Security Water Access Licences may, under some circumstances, pump water 'without debit' during these periods. For more information on pumping during supplementary flow events go to the relevant water sharing plan.
Supplementary flow events can occur in any regulated system at any time and therefore access is purely opportunistic. Supplementary events depend on the amount and location of rainfall and ensuing streamflow, and the catchment conditions at the time. They can be triggered overnight and last for a day or two, or a month to six months, depending on the river system and nature of the flow event.
The NSW Office of Water publishes timely details of supplementary flow announcements, and ensures equitable access to supplementary flows by water users along the river. Announcements are made by media release on this website. State Water notifies its customers directly.
Average annual water extractions in NSW
About 7,000 gigalitres of water is extracted on average each year in NSW. Of this, 70-80 per cent is used for irrigated agriculture. Around 6,000 GL (over 80 per cent) is extracted on average from regulated rivers which have flows controlled by large rural water storages operated by State Water, followed by groundwater which is mainly from the major inland alluvial groundwater systems, with the remainder being from unregulated rivers, many of which are coastal.