Melbourne
19.4 Delivery to urban water system users

The volume presented in the water accounting statements (353,309 ML) represents delivery of water from retail and rural water authorities to their end users for urban consumption in the Melbourne region during the 2011–12 year. This item represents the total delivery for the uses itemised in the following table.

Recycled water supplied by Melbourne Water to the Western Irrigation District and the Eastern Irrigation Scheme is reported at line item 19.6 Urban water discharge to irrigation schemes.

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 recycled water 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.

In the Melbourne region, wastewater treatment plants located within the region produce the majority of recycled water (see 'Wastewater System Overview' for further information). A very small volume of recycled water (237 ML : 11.21) is received from external organisations to supplement Melbourne's recycled water system.

During the 2011–12 year, approximately 70% of the recycled water produced (including the recycled water received from external organisations) was used on-site at wastewater treatment plants throughout the Melbourne region.  Of the recycled water used on-site, approximately half that volume (14,876 ML) was recirculated back into the wastewater system (and therefore not reported in the water accounting statements). The remaining recycled water used on-site was for irrigation/outdoor purposes or in-process and reported at line item 19.4.

The remaining recycled water produced in Melbourne was supplied for use; 8,415 ML was supplied to urban water system users [19.4]; and the remaining volume (3,089 ML) was supplied to either the Eastern Irrigation Scheme or Werribee Irrigation district [19.6].

The following figure presents the inflows and outflows associated with the recycled water system. A small misbalance (1.1%) is shown, due to the difference between the volume of recycled water available for supply and the volume of recycled water supplied for use. The misbalance can be attributed to metering inaccuracies, unaccounted losses and inaccuracies in the estimation of the recycled water on-site in process use.

For more detail on a particular flow associated with the recycled water system, refer to the line item notes. Note that volumes annotated with a * indicate flows between urban sub-components and are not reported in the 2012 Account.  As such, these flows do not have an associated line item number or note.

Schematic diagram of water inflows and outflows for Melbourne's recycled water system during the 2011–12 year. Line item numbers are provided in brackets.

The volume of water delivered to end users from City West Water was the sum of the following components.

City West Water has over 320,000 meters: residential meters are read on a quarterly basis. Generally, non-residential customers consuming greater than 10 ML per annum are read monthly and those that consume less than 10 ML are read quarterly.

Volumes are derived from monthly and quarterly meter readings, which are used to bill non-residential and residential customers. City West Water's Gentrack billing system collates all meter readings from residential and non-residential customers.

Commercial, industrial and municipal uses

The volume of recycled water supplied is derived from daily meter readings. This volume includes the metered volume of recycled water used at the Sunshine Golf Club for irrigation and recycled water supplied for industrial and education (school) use.

On-site in-process use (not-recirculated)

The volume of recycled water used on-site in-process at the Altona Wastewater Treatment Plant is derived from daily meter readings.

Volumes are only applicable to water use within the City West Water service area inside the Melbourne region. There was no residential supply to Little River during the 2011–12 year.

The uncertainty is +/– 5% according to meter specifications.

Commercial, industrial and municipal uses

The uncertainty is +/– 5% according to meter specifications.

On-site in-process use (not-recirculated)

The uncertainty estimate was not quantified.

The volume of water delivered to end users from Melbourne Water was the sum of the following components.

Notably, the volume reported for Melbourne Water excludes recycled water produced at Melbourne Water's Eastern and Western treatment plants and supplied to urban water authorities South East Water and City West Water. The subsequent supply of recycled water to customers by South East Water and City West Water is shown for each authority's respective quantification approaches.

Recycled water for other urban use

The recycled water volume of 9 ML was supplied from Melbourne Water's Western Treatment Plant to Southern Rural Water for the Werribee tourist precinct use. Recycled water supplied to Southern Rural Water (and other urban water authorities) is measured with magnetic flow meters at the interface of Melbourne Water and the receiving authority. The Western Treatment Plant logs data daily and reports quarterly.  The Eastern Treatment Plant logs data daily and reports quarterly.

Recycled water on-site outdoor/irrigation use

Recycled water was used on-site at Melbourne Water's Western Treatment Plant for irrigation, for discharge to Lake Borrie wetlands (Ramsar listed) as conservation flows and for indoor purposes. Ultrasonic level transmitters are used to measure on-site recycled water use at Melbourne Water's Western Treatment Plant, which logs data daily and reports quarterly.

The volume of recycled water used on-site for in-door purposes is included in the volume reported as on-site outdoor/irrigation usage as these volumes could not be separated.

Recycled water for other urban use

Magnetic flow meters are are assumed to have an accuracy of +/– 2%.

Recycled water on-site outdoor/irrigation use

Ultrasonic level transmitters are assumed to have an accuracy of +/– 10%.

The volume of water delivered to end users from South East Water was the sum of the following components.

The volume of potable water supplied for use is derived from quarterly meter readings (some larger users have monthly meter readings). Most of the meters were located at property boundaries.

The volume of non-potable water supplied for use is derived from quarterly meter readings. The volume reported includes non-potable supply for residential, commercial, industrial and municipal uses as it was not possible to separate the uses. Most of the meters were located at property boundaries.

Commercial, industrial, municipal, agricultural/individual irrigation use
The volume of recycled water supplied for use is derived from quarterly meter readings.

On-site outdoor/irrigation use
The volume of recycled water used on-site for outdoor purposes at South East Water's Mornington (Mount Martha) Sewage Treatment Plant is metered daily.

On-site in-process use
The volume of recycled water used for on-site in-process use at South East Water's sewage treatment plants is metered daily.

• Assumes meters and readings are accurate.
• Data reported from 01 July 2011 – 30 June 2012 are based on the four quarterly readings on each property. The water year for properties read early in the cycle starts in April and are billed in July. Later readings in the cycle have a meter year that starts in June and is billed in September.
• Some quarterly meter readings are estimated (due to issues such as meter inaccessibility) and will be adjusted in following periods.

Assumes meters and readings are accurate.

Reliability and accuracy is +/– 5% – i.e. Grade 2 (WIRA 2012).

The uncertainty is estimated to be +/– 5% (WIRA 2012).

Residential use

The volume of potable water supplied for residential use (excluding Woodend supply) was derived from monthly and four-monthly meter readings of potable water use. It was calculated based on the assumption that 84% of the total potable water supplied was for residential purposes and subsequently deducting the water loss component associated with residential supply. Meter's are located on individual's properties.

Commercial, industrial and municipal use

The volume of potable water supplied for commercial, industrial and municipal use (excluding Woodend supply) was derived from monthly and four-monthly meter readings of potable water use. It was calculated based on the assumption that 16% of the total potable water supplied was for residential purposes. Meter's are located on individual's properties.

The volume of non-potable water supplied for commercial, industrial and municipal use (excluding Woodend supply) was derived from meter readings of Individual Water By Agreement Customers.

Residential use

The volume of recycled water supplied for residential use (excluding Woodend supply) was derived from monthly meter readings from a meter located at the outflow from the class tank. Non-residential recycled water use (see below) was subtracted from the total metered outflow to provide the volume of recycled water supplied for residential use. Meters are read daily.

Commercial, industrial, municipal, agricultural/individual irrigation use

This item represents the total metered volume of recycled water supplied for commercial, industrial and municipal uses. Meters are located at customer properties and are read monthly.

Residential use

Total volume was approximated based on the meter readings and assuming 84% of potable water is supplied for residential use.

Commercial, industrial and municipal use

Total volume was approximated based on the meter readings and assuming 16% of potable water is supplied for non-residential use.

The uncertainty estimate is +/– 5% in accordance with Summary Audit Report – October 2010 (Essential Services Commission 2010). 

In accordance with the manufacturer's annual bulk meter test.

Customer usage is calculated as the difference between total water received and estimated non-revenue water volume, and is then divided into residential and non-residential components in the same ratio as the customer-billed volumes.

The volume of non-potable water supplied for use was derived from meter readings for residential and non-residential customers who have unchlorinated water service agreements.

Residential use

The volume of recycled water supplied to the Range Estate from Brushy Creek Local Treatment Plant was taken from the onsite bulk meter at the estate site.

Commercial, industrial, municipal use

The volume of recycled water supplied for commercial, industrial and municipal uses is derived from meter readings. It is the balance of the recycled water supplied to Urban/Industrial customers.

Agricultural/individual irrigation use

This item represents the metered volume of recycled water supplied from the Wallan Local Treatment Plant for agricultural use.

On-site in-process use (no-recirculation)

The volume of recycled water used on-site in-process is metered at all Yarra Valley Water's local treatment plant.

• customer usage in the reporting period is the difference between the total water received and the estimated level of nonrevenue water
• residential and non residential usage volumes are in the same proportion as billed and metered volumes.

• billed volumes over the four quarters provide an adequate estimate of water used in the reporting period.

The uncertainty estimate was not quantified.

The uncertainty was estimated to be –/+5%.

In the 2011 Account, urban water supply to the Western Irrigation District and the Eastern Irrigation Scheme was reported as part of line item 19.4 'Delivery to urban water system users'.

In the 2012 Account, urban water supply to irrigation districts/schemes within the Melbourne region at line item was reported at line item 19.6 Urban water discharge to irrigation scheme, in order to be consistent with the classification of urban water supply to irrigation schemes applied to the other regions of the National Water Account.

In addition, in the 2011 Account recycled water used on-site (not recirculated) was not reported. This may include recycled water used for on-site irrigation, indoor use (toilet flushing) or in-process (e.g. cleaning/watering down floors). These items represent urban water uses and outflows from the urban water system, therefore in the 2012 Account these volumes were reported at line item 19.4 'Delivery to urban water system users'. This does not include recycled water which is recirculated back through the wastewater/ recycled water system.

Consequently, the volume has been restated from 343,166 ML (as published in the 2011 Account) to 352,622 ML as shown in the following table.