Melbourne
Future outlook

Table 1 shows that there is a surplus of available water assets over water liabilities and future water commitments that are expected to be settled within 12 months of the reporting date.

¹Dead storage volume for surface water storages

²Average volume from 2009–10 to 2013–14: surface water diversions for individual users

³Average volume from 2009–10 to 2013–14: surface water transfers made under inter-region commitment

⁴Average volume from 2009–10 to 2013–14: groundwater extractions for individual users

⁵Average volume from 2009–10 to 2013–14: surface water diverted to the urban water system

⁶Average volume from 2009–10 to 2013–14: water delivered from outside the region

The volumes reported for future water rights and future water commitments are indicative only. The volumes presented in Table 1 were estimated from the average diversions and extractions in the previous five years. The actual volume of water delivered under these future water rights and future water commitments will depend on climatic conditions and demand.

Above average rainfall was experienced in the Melbourne region in both 2010–11 and 2011–12, increasing water availability and corresponding to a reduction in demand on water resources. These wetter conditions also enabled surface water storage levels to recover considerably. Consideration of diversions and extractions from these two years is likely to result in an underestimate of expected diversions and extractions for an average rainfall year.

Rainfall for the 2013–14 period was below the long-term average. Therefore the commitments stated in Table 1 are likely to be slightly under-estimated and the surplus after the commitments is likely to be a slight over-estimate of available water assets. 

Although it was not possible to quantify future inflows, it is expected that with current storage levels even below average inflows will meet the demands of future water commitments. The Victorian desalination plant at Wonthaggi was commissioned in December 2012 and is now another source for future urban water supply when required.

The purpose of this note is to report on possible water asset and possible water liabilities for the region. Possible (or contingent) water assets and water liabilities arise from past events and may be confirmed if future events (customer use) occur that are not fully under the control of the region's management.

The non-extractable portion of groundwater in the region (volume unknown)

Sustainable yields have been estimated for all groundwater resources within Victoria, in the context of the permissible consumptive volumes (PCV). These were determined by the Victorian Department of Environment and Primary Industries and represent the long-term average annual volume permitted to be extracted from aquifers within the Melbourne region. The limits are set to ensure groundwater is maintained at a sustainable level and are sufficient to maintain groundwater dependent ecosystems within the region.

The methods used to determine sustainable yields varied across the State according to the characteristics of the aquifers being investigated, and in many cases the full volume of the aquifer cannot be accurately quantified.

Water resource managers within the Melbourne region must adhere to the PCV extraction limitations for groundwater resources in the Melbourne region. The combined volume of the PCV has been recognised as a water asset in the National Water Account 2014. The volume of water that is beyond this extraction limit is considered a contingent water asset in the Melbourne region; however, there is currently not enough information available regarding the aquifers in the region to allow for a volumetric estimate.

Potable and nonpotable water for urban use (362,000 ML): Urban water retail authorities within the Melbourne region supply potable and nonpotable water to customers throughout the region. Water providers maintain water within distribution pipes for the delivery of water to the city but the actual delivery of water is determined by the customers when they turn on the tap. During the 2013–14 year, 363,157 ML of potable and nonpotable water was supplied to residential customers within the region. Notwithstanding any major changes, it is expected that a similar volume of water (362,000 ML; the average of the previous two water years) will need to be diverted from surface water in the 2014–15 year.

Water for irrigation use (10,000 ML): Southern Rural Water provides water to the Bacchus Marsh and Werribee irrigation districts in the Melbourne region; however, the actual delivery of the water is contingent on the irrigators of the Melbourne region drawing water from the system. It is estimated that 10,000 ML will need to be delivered in the 2014–15 year.