Melbourne: Water stores
- Below-average rainfall during most of the year contributed to low runoff across the region and a decrease in storage volumes.
- The reduced production of desalinated water meant that there was more reliance on inter-region transfers from the Thomson Reservoir for urban water supply compared to last year.
For a water balance of each of the region's water stores for the 2017–18 year scroll down this page or click on the links below:
Surface water store
| Description | Volume (ML) | |
| Opening surface water store | 555,653 | |
| add | Inflows | 1,083,211 |
| less | Outflows | 1,261,509 |
| add | Balancing item | 131,897 |
| Closing surface water store | 509,252 | |
- The volume of surface water in the region decreased from 555,653 ML at 1 July 2017 to 509,252 ML at 30 June 2018.
- The balancing item is 26% of the closing surface water store and is primarily attributed to uncertainties associated with the runoff and the river outflow estimates (see Methods).
Surface water flows
Figure S5 Water inflows and outflows for the surface water store during the 2017–18 year
- The largest natural water flows were runoff and outflow. Both were below average compared to previous years, reflecting the relatively poor rainfall conditions across the region during most of the year (see Climate and water).
- The largest water transfer in the region (delivery: inter-region agreement) primarily comprised transfers from Thomson Reservoir. The delivery of water from Thomson Reservoir increased by around 50% from last year, which is mainly due to a reduction in desalinated water supply for the region.
- Total surface water diverted in the region was 482,191 ML.
- 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.
- Approximately 2% of the total diversion was for individual users under an allocation; 3% was for non-allocated individual users and less than 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
| Description | Volume (ML) | |
| Opening groundwater store | 38,619 | |
| add | Inflows | 212,730 |
| less | Outflows | 153,431 |
| add | Balancing item | (59,299) |
| Closing groundwater store | 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.
- The relatively 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.
Groundwater flows
Figure S6 Water inflows and outflows for the groundwater store during the 2017–18 year
- The largest groundwater inflow was recharge: landscape, which accounts for 55% of the total groundwater inflows. Recharge from landscape was less than the previous year, reflecting the below-average rainfall and streamflow conditions across the region, particularly during the winter–spring months (see Climate and water).
- Total groundwater extracted in the region was 21,082 ML.
- More than 99% of the total groundwater extracted was used by individual users; less than 1% was for the urban water system.
- For a more detailed description of the water usage in the region, and the associated entitlements, see the Groundwater rights note
Urban water system
| Description | Volume (ML) | |
| Opening urban water system | 29,026 | |
| add | Inflows | 820,043 |
| less | Outflows | 815,164 |
| add | Balancing item | (5,486) |
| Closing urban water system | 28,419 | |
- 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 S7 Water inflows and outflows for the urban water system during the 2017–18 year
Water supply inflows
Figure S8 Water sources and total volume sourced for the Melbourne's urban water system during the 2017–18 year compared with the previous seven years
- Total inflows to the water supply system was 458,780 ML, 5% higher than last year.
- Inter-region water supply increased from last year. The decrease in production of desalinated water from the Wonthaggi Desalination Plant, as approved by the Victorian Government in May 2017, meant there was more reliance on inter-region transfers from the Thomson reservoir for urban water supply.
- Net surface water diversion to the urban system, which excludes desalinated water and inter-region water delivered to the surface water store, made up approximately 70% of total urban supply, which was similar to last year.
Wastewater and recycled water inflows
- Wastewater collected was 361,263 ML during the 2017–18 year.
Water supply outflows
Figure S9 Outflows from the water supply system
- The majority of water supply outflow was supply system delivery: urban users.
- 12% of the total outflow from the urban supply system was related to losses, similar to last year. Losses have decreased during the past two years compared to previous years 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 S10 Outflows from the wastewater and recycled water systems
- 15% 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.