11.12 Entitled diversion of allocated surface water to urban water system
a. Surface water diverted to the urban water system in the 2011–12 year
The volume reported in the water accounting statements (374,198 ML) represents the volume of water diverted from surface water for distribution via the urban water supply system under the various bulk entitlements held by Melbourne's retail water authorities, including Western Water. The volume reported includes:
- Bulk water supplied by Melbourne Water to the City West Water, South East Water and Yarra Valley Water from the Yarra, Tarago and Bunyip rivers and to Western Water from the Melbourne Headworks system.
- Surface water diverted from the Maribyrnong and Werribee river basins by Western Water under various bulk entitlements. Surface water is primarily diverted from storages managed by Southern Rural Water, but also includes diversions from smaller storages operated by Western Water.
Refer to line item 3.7 Urban claim on surface water for more information on these bulk entitlements.
The following table shows the volumes of surface water diverted for urban water supply by Melbourne Water and Western Water during the 2011–12 year.
|Authority||2012 Volume (ML)|
|Melbourne Water—bulk water supplied to retail water authorities
|Western Water—surface water diverted from the Maribyrnong and Werribee rivers
The volume of surface water diverted for bulk water supply by Melbourne Water is derived from the volume of water supplied to the retail authorities accounting for losses between the point of diversion and the point of supply to the authorities. This is explained in more detail in the quantification approach.
The volume of surface water diverted by Western Water is the metered volume at various offtake points. This is explained in more detail in the quantification approach.
The volume reported does not include water delivered by Melbourne Water to Gippsland Water (see 17.14 Surface water transfer under inter–region commitment).
Melbourne Water reports estimated proportions of water released from each of the seasonal reservoirs as an indication of the proportion of water intake from each reservoir to supply the total volume of bulk water (see following table).
|Release location||Percentage of total released|
|Yarra Valley (small treatment plants)||<1%|
b. Urban water supply system overview
The urban water supply system is one of three sub-components of Melbourne's urban water system. The three sub-components are the:
- Urban water supply system
- Wastewater system
- Recycled water system.
During the 2011–12 year Melbourne's urban water was sourced exclusively from surface water [11.12]; however in some years a very small proportion is sourced from groundwater [11.13]. While a desalination plant has been built to supplement Melbourne's urban water supply, this was not operational during the 2011–12 year.
Urban water consumption [19.4] of potable and non-potable water was 330,632 ML during the 2011–12 year, representing almost 90% of all urban water supply system outflows. A very small volume of water was transferred out of the region via normal operations in Western Water's service area [19.11]. Non-revenue water, including pipes bursting [19.2], background leakage [19.3] and other losses [19.20], made up the remaining urban water supply system outflows.
The following figure shows all the inflows and outflows for the urban water supply system. For more detail on a particular flow associated with the urban water supply system, refer to the line item notes.
Schematic diagram of water inflows and outflows for Melbourne's urban water supply system during the 2011–12 year. Line item numbers are provided in brackets.
A small misbalance (0.1%) is shown in the previous figure and can be attributed to possible differences in metering accuracies and unaccounted losses associated with water intake and supply.
The total volume of surface water diverted for bulk water supply was calculated from the following two components:
- Volume of potable and non-potable water supplied to the retail water authorities
- Volume of losses from the potable water system.
|Component||Individual items||2012 Volume (ML)|
|Total volume of water
provided to the urban
retail water authorities
by Melbourne Water
|Potable water provided to City West Water||96,338|
|Potable water provided to South East Water||129,844|
|Potable water provided to Yarra Valley Water||133,646|
|Potable water provided to Western Water||5,108|
|Non-potable water provided to Yarra Valley Water—water taken from Maroondah aqueduct as direct supply to customers||272|
|Non-potable water provided to South East Water—water taken from Bunyip River as direct supply to customers||64|
|Subtotal—volume provided to urban retail water authorities||365,272|
|Total volume of
losses and leakage
|Loss of potable water from major pipes—line item 19.2||129|
|Loss of potable water due to minor leaks—line item 19.2||20|
|Loss of potable water through service reservoir and tank dewatering—line item 19.20||580|
|Loss of potable water through operational activities—line item 19.20||1,772|
|Subtotal—losses from the potable water system||2,501|
Volumes were calculated using the weekly metered volume of bulk water supplied by Melbourne Water to urban retail water authorities. Metered volumes are based on Melbourne Water bulk meters.
Assumptions, limitations, caveats and approximations
In the above tables, meters are generally ultrasonic flow meters for larger pipes (greater than 600 mm diameter) and magnetic flow meters for smaller pipes (less than 600 mm diameter). Both types of meters have an accuracy of +/– 1% as reported by the manufacturers.
|Surface water intake point||Water Filtration Plant||2012 Volume (ML)|
|Forster and Wright reservoirs||Romsey||0
|Garden Hut Creek Reservoir||Lancefield1||168|
|Macedon and Mt Macedon storages||Reservoir C
|Merrimu and Djerriwarrh reservoirs||Merrimu2||5,599|
|Pykes Creek Reservoir||Myrniong||39|
1–2 This volume included non-potable and potable water supplied to users.
Assumptions, limitations, caveats and approximations
Uncertainty is +/– 5% in accordance with the manufacturer's annual bulk meter test.
In the 2011 Account, the following volumes were omitted from this line item:
- volume of surface water diverted by Western Water from Garden Hut Creek Reservoir (Lancefield WFP), Macedon storage, Wright Reservoir (Romsey Creek WFP) and Kerrie Reservoir (Romsey WFP)
- volume of potable water system losses from the calculation of the volume of surface water diverted for bulk supply
- volume of surface water diverted by Melbourne Water and subsequently supplied to Southern Rural Water for the Bacchus Marsh Irrigation district (This volume is zero in the 2012 Account).
In the 2012 Account, this omission was rectified from the 2011 Account to provide improved and more accurate information to users.
Consequently, the volume has been restated from 353,431 ML (as published in the 2011 Account) to 355,241 ML as shown in the following table.
|Component||Individual item||2012 Account volume
at 30 June 2011 (ML)
|2011 Account volume
at 30 June 2011 (ML)
|Total volume of bulk water provided to the urban retail water authorities by Melbourne Water||Potable water provided to City West Water||92,562||92,562|
|Potable water provided to South East Water||123,390||123,390|
|Potable water provided to Yarra Valley Water||127,314||127,314|
|Potable water provided to Western Water||7,881||7,881|
|Non-potable water provided to Yarra Valley Water—water taken from Maroondah aqueduct as direct supply to customers||307||307|
|Non-potable water provided to South East Water—water taken from Bunyip River as direct supply to customers||72||72|
|Subtotal—volume of bulk water provided to urban retail water authorities||351,526||351,526|
|Potable water provided to Southern Rural Water via Western Water for supply to irrigators in the Bacchus Marsh Irrigation District||46||0|
|Total volume of losses and leakage||Loss of potable water from major pipes— line item 19.2||183||0|
|Loss of potable water due to minor leaks— line item 19.3||75||0|
|Loss of potable water through service reservoir and tank dewatering—line item 19.20||28||0|
|Loss of potable water through operational activities—line item 19.20||781||0|
|Subtotal – losses from the potable water system||1067||0|
|Total volume of surface water diverted by Western Water||Baringo Creek||33||0|
|Garden Hut Creek Reservoir for treatment at Lancefield WFP||155||0
|Macedon and Mt Macedon storages—for Reservoir C||175||0
|Merrimu and Djerriwarrh reservoirs—for treatment at Merrimu WFP||1,817||1,804|
|Pykes Creek Reservoir—for treatment at Myrniong WFP||28||28|
|Forster and Wright reservoirs—for treatment at Romsey WFP||14||0
|Kerrie Reservoir—for treatment at Romsey WFP||307||0
|Rosslynne Reservoir—for treatment at Rosslynne WFP||73||73|
|Subtotal—volume of surface water diverted by Western Water||2,602||1,905|