Melbourne: Water stores
An increase in annual rainfall from the previous year contributed to increased runoff across the region and an increase in surface water storage. The increase in the region's surface water availability, as well as supply from the Wonthaggi Desalination Plant, meant there was much less reliance on inter-region transfers from the Thomson Reservoir for urban water supply.
For a water balance of each of the region's water stores for the 2016-17 year scroll down this page or click on the links below:
Surface water store
| 2017 ML | 2016 ML | |
| Opening surface water store | 515,682 | 522,005 |
| Inflows | 2,111,245 | 1,221,354 |
| Outflows | (1,860,291) | (1,308,903) |
| Balancing item | (210,983) | 81,226 |
| Closing surface water store | 555,653 | 515,682 |
- The volume of surface water in the region increased from 515,682 ML at 1 July 2016 to 555,653 ML at 30 June 2017.
- The balancing item of 210,983 ML is 38% of the closing surface water store. The balancing item is primarily attributed to uncertainties associated with the runoff and the river outflow, which are estimated from rainfall-runoff and river water balance models (see Methods).
Surface water flows
Figure S5 Water inflows and outflows for the surface water store during the 2016–17 year
- The largest natural water flows were runoff and outflow. Both were much higher than the previous year, reflecting the improved rainfall conditions across the region (see Climate and water).
- The largest water transfer in the region (delivery: inter-region agreement) comprised transfers from Thomson Reservoir (86,383 ML) and transfers from Silver and Wallaby Creeks (3,058 ML). The delivery of water from Thomson Reservoir decreased by 65% from the previous year, which can be attributed to the increase in the region's surface water availability, as well as the production of desalinated water in the region for the first time.
Figure S6 Volume received by water authorities under surface water allocation diversion to the urban water system during the 2016–17 year
- Total surface water diverted in the region was 457,095 ML, marginally less than the previous year.
- More than 95% of the total surface water diverted was for urban system supply. This includes the delivery of water by inter-region agreement from the Thomson Reservoir, as well as the delivery of desalinated water from the Wonthaggi Desalination Plant.
- 2% of the total diversion was for individual users under an allocation; 2% was for non-allocated individual users and 1% was for inter-region transfer.
- For a more detailed description of the water usage in the region, and the associated entitlements, see the Surface water rights note.
Groundwater store
| 2017 ML | 2016 ML | |
| Opening groundwater store | 38,619 | 38,619 |
| Inflows | 264,971 | 356,667 |
| Outflows | (185,878) | (149,266) |
| Balancing item | (79,093) | (207,401) |
| Closing groundwater store | 38,619 | 38,619 |
- The volume of groundwater in the region is equivalent to the permissible consumptive volume, which is the legal extractable limit and, therefore, remains unchanged from year to year.
- Such a high balancing item is primarily attributed to the fact that key items such as groundwater discharge to the landscape and to the rivers cannot currently be quantified in the account.
Groundwater flows
Figure S7 Water inflows and outflows for the groundwater store during the 2016–17 year
- The largest groundwater flow was recharge: landscape, which accounts for over 75% of the total groundwater inflows. Recharge to landscape was higher than the previous year reflecting the improved rainfall and streamflow conditions across the region, particularly during the winter and spring months (see Climate and water).
Figure S8 Groundwater extractions for individual use within the Melbourne region during the 2016–17 year
- Total groundwater extracted in the region was 20,372 ML, similar to the previous year.
- More than 99% of the total groundwater extracted was used by individual users; less than 1% was for the urban water system.
- The total groundwater extracted did not include all possible extraction under stock and domestic rights due to a lack of available data; therefore, the total volume is likely to be an underestimation.
- For a more detailed description of the water usage in the region, and the associated entitlements, see the Groundwater rights note
Urban water system
| 2017 ML | 2016 ML | |
| Opening urban water system | 29,828 | 28,740 |
| Inflows | 814,767 | 797,013 |
| Outflows | (810,834) | (792,857) |
| Balancing item | (4,735) | (3,068) |
| Closing urban water system | 29,026 | 29,828 |
- The volume of water in the Melbourne region's urban water system includes water held in wastewater treatment plant lagoons and holding basins. This volume changes little from year to year.
- The balancing item is likely attributed to metering inaccuracies, unaccounted losses, and inaccuracies in the estimation of certain volumes (see Methods).
Urban water system flows
Figure S9 Water inflows and outflows for the urban water system during the 2016–17 year
- A more detailed breakdown of the inflows and outflows of the urban water system components is provided in the urban water balance diagram.
Water supply inflows
Figure S10 Water sources and total volume sourced for the Melbourne's urban water system during the 2016–17 year compared with the previous six years
- Total inflows to the water supply system was 436,908 ML, a decrease of 2% from the previous year.
- Net surface water diversion to the urban system, which excludes desalinated water and inter-region water delivered to the surface water store, made up 69% of total urban supply. Net surface water supply was higher than the previous three years as the improved rainfall conditions across the region meant there was more surface water available to meet demand (see Surface water store).
- Desalinated water made up 11% of urban supply. This was the first year that desalinated water production from the Wonthaggi Desalination Plant occurred in the region.
- Inter-region water supply decreased by approximately 64% from the previous year. The increase in the region's surface water availability, as well as the production of desalinated water, meant there was much less reliance on inter-region transfers from the Thomson Reservoir for urban water supply.
Wastewater and recycled water inflows
- Wastewater collected was 377,859 ML during the 2016–17 year.
Water supply outflows
Figure S11 Outflows from the water supply system
- The majority of water supply outflow was supply system delivery: urban users.
- 10% of the total outflow from the urban supply system was related to losses, compared to 12% last year. The decrease in losses was mainly due to closer monitoring of night flows, as well as reduced response and repair times following pipe bursts.
Wastewater and recycled water system outflows
Figure S12 Outflows from the wastewater and recycled water systems
- 12% of the treated wastewater was recycled, most of which was recycled water delivery: urban users.
- Most of the remaining treated wastewater was discharge: sea.
- 5% of the total outflow was related to losses.