How do we account for water?

The Victorian Water Accounts presents an annual account of surface water, groundwater and water supply systems in Victoria.

This page outlines the basis for the information presented in each of the surface water, groundwater and water supply reports on this site.

It explains some important assumptions and limitations of the data in the accounts, which should be read in conjunction with the information in the reports.

The accounts are compiled with information obtained from:

• the Victorian Water Register (VWR)
• the Victorian Water Measurement Information System (WMIS)
• urban and rural water corporations
• the Essential Services Commission (ESC)
• the Murray Darling Basin Authority (MDBA)
• the Bureau of Meteorology (BoM)
• Department of Energy, Environment and Climate Action (DEECA) (for water supply system models)
• the Victorian Environmental Water Holder (VEWH)
• some major industrial users of water.

In this website, we report on surface water, groundwater and water supply via 8 types of water reports.

Surface water reports by:

• river basin
• statewide.

Groundwater reports by:

• groundwater catchment
• groundwater management unit
• statewide.

Water supply* reports by:

• water corporation
• water supply system (e.g. individual town or irrigation system)
• statewide.

* In previous Accounts, water supply systems were referred to as distribution systems instead. The meaning has not changed.

Correcting errors in the Victorian Water Accounts

Each year, the Victorian Water Accounts undergoes rigorous review by a number of subject matter experts within DEECA. However, on rare occasions, an error in the accounts is identified after an account has been approved and published.

In the event that an error is identified after an account has been published, the following process will apply:

• Consistent with the Bureau of Meteorology’s National Water Accounting Standards, the incorrect table and chart in the account will not be changed to the updated data. Instead, a correction will be made to ‘previous year’ numbers in the subsequent year’s account.
• A written erratum note will be added alongside the incorrect table in the prior published account to indicate to users that a correction to this number has been made in a subsequent report. This enables users to seek and use the latest available information in their data analysis.

Uncertainty in water accounting

The Victorian Water Accounts are a wide ranging report with data points from a variety of information sources. Many of these are directly measured via meters or gauges, and have relatively high confidence. Others are modelled or estimated, and we may have lower confidence in these values. The figures provided in the Accounts represent the best estimates based on the data and models available at the time. Models and methods are periodically reviewed and updated to improve confidence.

Users should note that higher uncertainty exists in the following figures and circumstances in particular:

• Water harvested, used and lost by small catchment dams (farm dams) - these figures are modelled, taking into account the climate of the year, but the way farm dams impact on the water balance is complex and uncertain due to the influence of numerous variables, including cropping area, crop pattern and irrigator behaviour. The method used in the accounts also makes assumptions to differentiate between small catchment dams for commercial or irrigation applications, and those used for stock and domestic purposes.
• In-stream infiltration to groundwater, flows to floodplain and evaporation: this 'loss' figure is modelled for some river basins where an appropriate model is available, but its ability to accurately represent overbank and floodplain inundation dynamics is limited. Additionally, surface water-groundwater interactions represent one of the most complex hydrological processes to model. Even sophisticated models may struggle to accurately capture the intricacies of this relationship, leading to inherent uncertainties in the results.
• Streamflow, during high flow events: when flows in waterways exceed the rating curves used to convert stream depth to flow volume, uncertainty increases. Established methods can be used to estimate flows using other available data, but during significant floods it can be challenging to confidently estimate flows. This also impacts the losses and end of basin outflows in the water balance.
• Catchment inflow: in all basins except for the Murray, catchment inflow is the balancing item in the water balance. This means that any uncertainty in any other water balance items will also be reflected in this figure. Catchment inflow is also reported as total streamflow and total available water for surface water systems.

While volumes in the accounts are presented to the nearest megalitre or gigalitre, these values should be interpreted in the context of the above uncertainty caveats.

Some volumes are unable to be estimated at all, and are not included in the Accounts. Examples include:

• Unlicensed diversions for domestic and stock use.
• Rainfall and evaporation from some storages where suitable nearby gauging sites are unavailable.

The basin water accounts track surface water when it:

• appears as inflows to a river or stream
• is diverted or lost from the rivers and streams of the basin
• flows from the basin to another basin
• flows from the basin to the sea
• flows to a terminal lake inside the basin.  

Victoria’s river basin boundaries can be seen below. The flow of surface water (and data about the flow) generally aligns well with river basin boundaries, except where water is diverted from a waterway in one river basin and is then used in another.

Figure 1: Victorian river basins

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The Victorian Water Accounts use the river basins defined by the former Australian Water Resources Council (AWRC), except for the Murray basin. In the accounts the Murray basin includes the Upper Murray basin as defined by the AWRC and the areas in Victoria that are supplied from the Murray River downstream of Lake Hume.

The Victorian Water Accounts report on surface water availability and use at both local (river basin) and statewide scales. The river basin local reports provide the water accounts for Victoria’s 29 river basins for the water year. The statewide page provides a high-level summary of the data across all basins, and provides some additional information that is best reported at a broader scale.

River basin local reports

Each local report has a brief description of the area and covers the following sections:

• Climate
• River basin water balance
• Entitlements and compliance
• Water for the environment
• Management responsibilities

Climate

This section describes the rainfall received for the water year, compared to average rainfall. The baseline period used to calculate average rainfall is 1975 to the current year.

River basin water balance

The water balance is the principal water accounting tool in the Victorian Water Accounts. It provides a statement of the water flows in a basin for the water year. Here, the sum of the outflows from the basin equals the sum of the inflows, minus the water accumulated in the area.

A water balance is not presented for the Mallee and Millicent Coast basins, as a lack of significant surface water resources in these basins means there is insufficient data available to prepare a water balance. In the northern basins, it is possible that the volumes presented in the water balance are not consistent with the MDBA’s cap compliance reporting due to different accounting methods.

Some explanations and assumptions about components of the water balance are provided below. 

Storages

Change in storage is calculated as the difference between the volume in storage at the start of the year and at the end of the year.

Rainfall on, and evaporation from, major storages are reported as inflows and outflows respectively. These are estimated based on local rainfall and evaporation data, and the surface area of the storages.

Catchment inflow less regulated releases is a measure of the change in storage during the year (excluding that from rainfall and evaporation). It can be negative, in the event that the storage is drawn down during the year.

In general, only on-stream storages with a total capacity of more than 1,000 ML are included in the water balance. Smaller storages are important locally, but generally not material to the total volume of water at a basin scale.

The volume of water in off-stream storages is not reported in the surface water balance. In some instances, this would result in double-counting water that has been diverted from rivers or extracted from groundwater.

Inflows

Catchment inflow

Catchment inflow represents the total volume of surface run-off from rainfall that becomes streamflow in the basin or is captured by small catchment dams.

Generally, a large portion of catchment inflow is the unaccounted-for item in the water balance. As a balancing item, it is calculated to be the difference between the total outflows and the known inflows of the river system.

The exception to this is the Murray basin, where catchment inflows are known; they include measured inflows from other river basins and to Victoria’s share of major Murray storages. In the Murray basin water balance, the balancing item is in-stream losses.

The volume of catchment inflow per basin also includes an estimate of the volume harvested by small catchment dams. See below for the small catchment dam accounting method.

Catchment inflows from the water balance are compared to the long-term average (1975 to current year) inflow for each basin. 

Transfers from other basins

Transfers from other basins are included in a basin’s water balance only if they are known to affect streamflows in the receiving basin.

If water transferred across basin boundaries is supplied directly into a water supply system and does not affect streamflows, it is considered as a diversion to an end use (for example, urban and irrigation district diversions). It is not accounted for as a transfer in the water balance.

Return flow from irrigation, environment, power stations or major industry

Return flows represent an inflow to the water balance where water is returned to the waterway after previously being diverted. These can be returned following different uses of water and are specified as such in the water balance line items. Return flows from irrigation are the outfalls from an irrigation system that return to waterways, while return flows from environment represent water returned after off-stream (e.g. wetland) environmental watering events. In the Latrobe basin, return flows are from power stations and major industry.

Treated wastewater discharged back to river

This item represents the volume of treated wastewater discharged from wastewater treatment plants back into waterways.

Volumes of wastewater produced, recycled for various uses and discharged to various receiving environments are provided per wastewater treatment plant in the local water supply reports.

Outflows

Urban diversions and irrigation district diversions

These items represent the total volume of water diverted from waterways by water corporations to supply urban customers, and customers in declared irrigation districts, respectively.

For the purpose of the basin water balances, water is accounted for at the point of diversion from the waterway and not at the point of use. For example, information about diversions to supply the Rochester Irrigation Area, located at the downstream end of the Campaspe basin, is accounted for in the Goulburn basin where the source of the supply is located.

Licensed diversions from regulated or unregulated streams

This item represents the volume of water diverted directly from waterways by licence holders. These diversions are reported separately for regulated and unregulated waterways or sections of waterway. Depending on the system, licensed diversions from regulated streams might be either licensed use via a water use licence in declared systems, or a take and use licence in non-declared regulated systems.

Licensed domestic and stock water users are assumed to divert their full entitlement volume unless otherwise reported by water corporations.

The water balance excludes diversions under private rights for domestic and stock use (under section 8 of the Water Act 1989), which do not require a licence. The volume associated with these rights is relatively small.

Environmental water diversions

This describes where environmental water is diverted from a waterway to off-stream wetlands or to a distributary river or creek (i.e. where the water does not return to the main river channel) under environmental entitlements. It does not include water use under environmental entitlements that was delivered in-stream – that volume is captured in ‘water passed at outlet of basin’ (explained below).

Small catchment dam use

This item represents the estimated volume of extractions from small catchment dams within a basin (see below for small catchment dam accounting methodology).

Net evaporation from small catchment dams

This item is the total estimated volume of evaporation minus direct rainfall from all small catchment dams’ surfaces.

In-stream infiltration to groundwater, flows to floodplain and evaporation (in-stream losses)

This item represents the volume of water that is lost from the waterway via natural processes and is not directly measurable. These losses are typically modelled (where models exist) as a proportion or function of gauged streamflow. The models used are listed in Table 1 below.

In the Murray basin, in-stream losses for the year are considered to be the unaccounted-for item in the water balance and are used as balancing items. In this instance, in-stream losses are determined to be the difference between the known outflows and the total inflows plus the net change in storage volume.

There are 10 basins (East Gippsland, Snowy, Tambo, Latrobe, South Gippsland, Yarra, Corangamite, Otway Coast, Hopkins and Portland Coast) where a suitable loss model does not exist, and in these basins in-stream losses are not included in the water balance.

Models used to derive in-stream losses

Table 1: In-stream loss models

Note: REALM is an acronym for Resource Allocation Model.

Water passed at outlet of basin

This item represents the total volume of water that flows out at the end of the basin, either to the ocean, other rivers, terminal lakes or, in the case of the Murray, Victoria’s share of flows crossing the South Australian border. The volume of water passed at basin outlets is estimated by using gauged streamflow data at a point as close to the basin outlet as possible. We then extrapolate that data to the basin area.

Small catchment dam accounting method

Small catchment dams harvest water from their local catchment. The presence of small catchment dams changes the hydrology in a basin by reducing the rate of overland flows (that is, surface run-off) and by altering evaporation and groundwater seepage. Small catchment dams reduce the volume of surface run-off that might otherwise become streamflows in a basin. Victoria models the volumes associated with small catchment dams via a small catchment dam interception model.

In the Victorian Water Account before 2016-17, the total volume of water harvested by small catchment dams was estimated from computer-based simulation modelling of the impact of small catchment dams on mean annual streamflows, based on estimates of the total volume of small catchment dams in a basin.

From 2017-18, the method used to estimate the usage, evaporation and harvested volumes from small catchment dams was improved. The key difference is that each dam identified in the GIS data has been individually modelled, to better reflect the water balance around the dam based on the climate for that year.

Volume harvested by small catchment dams

The amount is determined by calculating the water balance around each individual dam based on the annual climate including inflows, extractions, rainfall and evaporation. The total volume harvested is the difference between dam inflows and outflows. By aggregating volumes harvested by dams across each basin, we estimate how much water is harvested by small catchments over the course of the year.

Use by small catchment dams

The volume extracted — the volume used in each basin — is calculated by multiplying the estimated capacity of each dam by an extraction factor and reducing this number as necessary if the dam had insufficient inflows to actually supply the volume required.

Net evaporation

This volume is determined directly from a water balance calculated for each individual dam.

When rainfall is high and evaporation is low, this can be represented as a negative loss in the water balance.

Entitlements and compliance

This section presents the entitlement volumes, available water and compliance against entitlements in the basin for the water year.

Entitlement volumes

A table in each basin local report shows the volume of entitlements as of 30 June of each water year.

Entitlements provide the basis for how water is shared. The total volume of entitlements changes each year as new entitlements are issued or existing entitlements are modified. The total entitlement volume presented in these Accounts is the maximum amount that can be taken in any one year. The actual amount available to be taken in a particular year will differ within the entitlements summed, due to rules for allocating water which vary between entitlements, and to the seasonal conditions in that year. Some entitlements, often held by the environment and water authorities, do not have a specified annual volume. Those entitlements still provide for a share of the resource, however the Accounts do not report a volume for them.

Bulk entitlements specify a maximum volume of water that may be diverted over a given number of years. The annual entitlement volumes table provides the entitlement volume as the end of the water year and represents the maximum volume that may be diverted in any one year. Where the entitlement volume is an amount specified over more than one year, the total volume that may be taken over the period of the entitlement is shown in the notes. For example, the Gisborne-Barringo Creek bulk entitlement in the Maribyrnong basin specifies that up to 585 ML can be diverted in any one year, while the maximum volume that can be taken over any five-year period is 1,600 ML (320 ML annual average).

In the large, regulated systems, bulk entitlements are normally specified in one of two ways:

• source bulk entitlement: this is an entitlement to harvest water directly from a water source. Source entitlements typically cover multiple storages operated in an integrated way within a river basin. They also include obligations to divert or release water to supply primary entitlement holders (such as customers within irrigation districts, licensed diverters in regulated streams, water corporations that hold delivery bulk entitlements and environmental entitlements held by the VEWH).
• delivery bulk entitlement: this is an entitlement to be supplied with water from another water corporation’s dam within a water supply system which is regulated by the works of another water corporation.

The bulk entitlement volume for a source bulk entitlement will include the volumes supplied to delivery entitlement holders and other primary entitlement holders specified in the source bulk entitlement. To account for this, primary entitlements are presented inset as a part of the source bulk entitlement.

Entitlements to water also include rights granted to individuals (for example, water shares and take and use licenses). These are reported as a group of each entitlement types and show the total volume of licences issued per basin.

Unregulated licenses have been reported separately and include:

• take and use licenses – unregulated surface water, which includes all licence volume that is for water taken from the waterway. It includes licences to take from a waterway to fill an off-water dam (dams for which no harvesting from the catchment is possible)
• licenced small catchment dams – on-waterway, which includes licensed small catchment dams that are on-waterway; they harvest water from the catchment and do not take any water from the waterway.

Note that the volume of usage, loss and water harvested for small catchment dams is an estimate based on a small catchment dam interception model.

Available water and take under entitlements

A table in each basin local report shows the volume of water made available and taken under entitlements for each water year.

The components of the available water and use table – opening carryover, allocation issued, net trade in or out, spillable write-off, total water available and water taken – are described below.

Opening carryover: this item represents any water carried over from previous water year that could be taken.

Allocation issued: this item represents the water allocation made available under the entitlement in the water year. Individuals or authorities that hold water entitlements in Victoria are allocated water according to the volume and reliability of their entitlement and the available resource. For example, if entitlement holders with low-reliability water shares in the Thomson-Macalister system are allocated 25% of their entitlement, they will be allocated 25 ML for every 100 ML of low-reliability entitlement they own. This is available to use or trade.

Water issued and used under take and use licences is also represented as allocation in the allocation account balance tables. This allocation issued represents the volume that was available under licences throughout the water year. At a system level, that volume can be different to the entitlement volume at the end of the water year. Where licences have been cancelled during the year, the allocation volume presented may be greater than the entitlement volume as at the end of the water year.

The volumes may also be different as a result of temporary trading between systems. For example, temporary trade of licences can occur between unregulated and groundwater systems in the Ovens basin, which would affect the allocation volume issued to licences in the Ovens basin.

Net trade in or out: this item represents the volume of water traded into the basin, less the volume traded out of the basin.

Spillable write-off: in the Murray, Goulburn, Campaspe and Wimmera basins, some of the water carried over from the previous year can be deducted from customer accounts in the event that major storages spill (overflow). 

Total water available: this represents the volume of water that was available for use and trade in the water year. This item is the sum of opening carryover, allocation issued and the net of the in or out trade of water, less the spillable write-off.

Water taken: this item represents the volume of water used during the year under the entitlement. Where a source bulk entitlement exists, a total diversion is reported. This represents the volume of water diverted from the waterway to supply the primary entitlements specified in the bulk entitlement.

Compliance

The Victorian Water Accounts report entitlement compliance only at a whole-of-river-basin, rather than against individual entitlements.

Most extractions are metered. For more information about Victoria’s metering program, go to Keeping track of Victoria's water.

Compliance against water entitlements is reported in these accounts in three areas:

• entitlement issued: the volume of entitlements issued in a basin does not exceed formal caps or has not increased without appropriate approvals
• water taken: the volume of water taken during the year does not exceed the volume considered to be available for consumptive and/or in-stream use during that year
• bulk entitlement provisions: holders of entitlements do not breach any provisions that are documented in their bulk entitlement orders.

Water for the environment

This section describes the environmental watering sites in the basin and any environmental entitlements. It also summarises the volume of environmental water delivered for the water year.

Management responsibilities

This section details the relevant organisations in each basin and their management responsibilities.

Through this website you can view groundwater use and availability via groundwater local reports (select by catchment or management unit) or the groundwater statewide summary.

The groundwater catchment and groundwater management unit local reports are similar in nature.

Both types of groundwater local reportsinclude groundwater level trends, summaries of entitlements and use, restrictions on licensed use and management responsibilities.

Groundwater catchment local reports also include a high-level overview, and a summary of rainfall received.

Groundwater management unit local reports also include compliance against entitlements.

Groundwater catchment local reports

The main way we report on groundwater accounts in the Victorian Water Accounts is by groundwater catchment local reports. There are 20 groundwater catchments in total (Figure 2). A groundwater catchment approximates their respective surface water basin, with adjustments based on knowledge and assumptions about groundwater flow divides.

Figure 2: Victorian groundwater catchments

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Groundwater management unit local reports

We also provide local report accounts for each groundwater management unit (GMU). GMUs are smaller management units found within groundwater catchments. A groundwater catchment can include several GMUs.

The GMU local reports provide the accounts for Victoria’s 55 groundwater management units (Figure 3).

Figure 3: Victorian groundwater management units

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How to read groundwater local reports

Climate

This section describes the rainfall received over the groundwater catchment for the water year, compared to average rainfall. Rainfall can act as recharge for aquifers, where they are connected to the surface. 

The baseline period used to calculate average rainfall is 1975 to the current year.

Groundwater level trends

This section summarises 5-year trends in groundwater management units. Long-term trends in groundwater levels reflect differences between water flowing into (recharge) and out of (discharge) an aquifer and how much is taken for consumptive purposes.

Groundwater level trends in shallow aquifers are more likely to reflect more-rapid changes in annual recharge from either rainfall or discharge from irrigation, whereas confined aquifer trends may show a seasonal influence from pumping within a longer-term trend.

In the Accounts:

• groundwater level trends for groundwater management units (GMUs) have been determined based on five years' consistent monitoring data from key bores in the State Observation Bore Network
• trend determinations are made quarterly, and each reading is compared to previous readings in the same season (that is, a summer record is compared to previous summer records) to account for seasonality
• the reported trend for each quarter represents the change in level from five years before. If the level is similar it is considered stable, a higher level is rising and a lower level is declining.

Groundwater restrictions

This summarises any restrictions on licensed groundwater use in groundwater management units during the year. Some more general information about restrictions on groundwater licensed diversions is provided in Responding to water availability.

Entitlements and use

Groundwater entitlements and use is reported under 5 use types: urban, non-urban, power generation, domestic and stock, and salinity control.

• Urban use represents licences held by urban water corporations to supply towns. These are typically in the form of take and use licences, except for one groundwater bulk entitlement held by Barwon Water in the Otway-Torquay groundwater catchment.
• Non-urban use represents licences held for non-urban uses, including irrigation or commercial uses. Unlike for surface water, groundwater data is unable to distinguish between irrigation and commercial uses, so both are reported together.
• Power generation use represents licences held for the purposes of large-scale power generation.
• Domestic and stock use reports on estimated groundwater use for domestic and stock purposes, which is permitted without a take and use licence under section 8 of the Water Act 1989.
• Salinity control use reports on groundwater taken for the purposes of managing salinity.

The Entitlements and use section includes two sub-sections, Entitlement volumes and Available water and use.

Entitlement volumes contains a table and a chart outlining the total licenced entitlement volume for urban, non-urban and (where relevant) power generation use types, within each GMU as of 30 June for each water year.

The total volume of groundwater entitlements that are outside management units (i.e. not in a GMU) is also shown for groundwater catchments.

Available water and use contains a table outlining the following values, per use type per GMU for licensed use.

• Carryover is any water carried over from the previous year that could be taken. Carryover in a particular system is only available if the Minister for Water has made a declaration under section 62A of the Water Act 1989.
• Licensed volume allocated is the volume of water able to be taken and used under licences during the year. The licensed volume allocated may be different to the licensed entitlement volume because:
  • a restriction on water use might be in place in the GMU. For example, to manage the resource, licence holders in a given year might be restricted to a set percentage of their entitlement volume
  • licences may have been cancelled or temporarily traded during the year. This means the allocation volume may be greater or less than the entitlement volume. For example, temporary trade of licences can occur between GMUs in Victoria. This would affect the allocation volume issued to licences within those GMUs.
• Net trade is the volume of water traded in for use within the GMU, minus the water traded out of the GMU.
• Total water available is the volume of water that was available under licences to be taken in 2021-22. This is the sum of the first three components: carryover, water allocated and the net of the in or out trade of water.
• Water taken is the volume of water taken and used during the water year under licenses.

Note that total water available is distinct from the permissible consumptive volume (PCV). PCV represents the maximum volume that can be licensed and used in a GMU as declared by the Minister for Water. The total water available represents the overall volume that is available to licence holders in each individual year. The available volume may change from year to year because of carryover and/or trade.

Under available water and use, a chart is also provided showing the breakdown of use by type of use.

Compliance

Most groundwater extractions in Victoria are metered. The metering of licensed groundwater extraction supports responsible groundwater management. Information about Victoria’s metering program, go to the DEECA Water website.

In the Accounts, we report groundwater compliance at a whole-of-GMU scale, rather than against individual entitlements. Compliance against water entitlements is reported for GMUs in two areas:

1. entitlement issued: the volume of entitlements issued in the GMU does not exceed relevant permissible consumptive volume (PCV) or has not increased without appropriate approvals
2. water extracted: the volume of water taken under entitlements during the year does not exceed the total water available to licence holders.

PCV compliance is not assessed in the following five GMUs:

• Upper Ovens WSPA. A PCV is not required because the management plan prevents additional entitlements or an increase in entitlement volume being issued, except by trade
• Shepparton Irrigation Region GMA. There is no PCV as there is no limit on the total volume of shallow groundwater entitlement available
• West Goulburn GMA. There is no PCV, but there are individual zone caps set
• South West Limestone GMA. The PCV has not been gazetted
  • The South West Limestone GMA includes: the area of the former Nullawarre WSPA, Yangery WSPA, Hawkesdale GMA, Heywood GMA and the areas outside the former GMUs but included within the South West Limestone GMA area
  • The PCVs for the four GMUs have not been revoked and still apply. These are:
    • Nullawarre 22,741 ML
    • Yangery 14,352 ML
    • Hawkesdale 16,161 ML
    • Heywood 8,500 ML
• Stratford GMA. Current compliance assessment criteria are not applicable. Coal mine licences physically in the area are not assigned to the Stratford GMA.

For West Wimmera GMA, Wy Yung GMA, Nepean GMA, Rosedale GMA, Stratford GMA and Wa De Lock GMA, the PCV that applies is the sum of the PCVs for all zones within these GMAs.

Water supply local reports provide the accounts for all of Victoria’s rural and urban water supply systems, at both individual system scale and water corporation scale.

In previous Accounts, these were referred to as distribution systems rather than water supply systems. The meaning has not changed.

While surface water and groundwater pages in the Accounts describe the entitlements and use of water taken from river basins and groundwater aquifers, the water supply pages describe the movement of this water through the constructed supply systems that deliver water to users.

Water supply systems typically supply within irrigation districts or towns and urban areas. Some infrastructure services both of these end uses. On occasion, environmental entitlements are supplied using the water supply systems.

Providing water accounts for water supply systems enable water corporations and the community to understand where delivery-efficiency improvements to reduce losses can be most readily made.

Some information that was previously contained in the surface water accounts can now be found in the water supply system accounts. This includes recycled water accounting, and a summary of urban restrictions.

Water supply local reports

The water supply system water balance is the principal water accounting tool for these local reports. It provides a statement of the water flows in a water supply system for the water year, where the sum of the outflows from the system equals the sum of the inflows, minus the water accumulated in the system.

Each of Victoria's 18 water corporations have a page which provides water supply system accounts (under water deliveries) and recycled water accounts.

The water supply reports landing page allows users to select from lists of water corporations with urban, rural and common water supply systems. These are defined as follows.

Urban water supply systems primarily supply urban customers.

• They may supply a single town or a group of towns, and may also transfer water to other water supply systems.

Rural water supply systems primarily supply irrigation water.

• Some rural supply systems also supply other commercial customers, urban systems and domestic and stock water.

Common water supply systems are bulk or feeder systems that supply two or more water supply systems.

• They typically have few or no retail customers.
• Examples include Melbourne Water’s system, the Goldfields Superpipe (operated jointly by Coliban Water and Central Highlands Water) and the Waranga Western Channel (which supplies several irrigation and other systems, including the Goldfields Superpipe).

Some local water supply reports also provide accounts for combined water supply systems. These are systems that supply both urban and rural customers. Wannon Water and Grampians Wimmera Mallee Water both operate combined systems.

Water supply system water balances

Start and end volume in store

This represents the volume of water held in storages that are accounted for within the water supply system (for example, the account for Castlemaine water supply system includes water stored in McKay Reservoir) at the start and end of the financial year. In systems where this volume changes during the year, these volumes are an important part of the water balance.

On-stream storages (for example, Lake Eildon) are not considered to be part of water supply systems as they are already covered in river basin accounts. The bulk water entitlements that authorise water being taken from waterways serve as a guide to whether a storage is off-stream.

As far as possible, the accounts have been prepared on a consistent basis, while recognising the substantial differences between systems.

Inflows

The inflows section of the water balance shows all water flows into the water supply system. These inflows may be direct from surface water, from groundwater or from another water supply system. Where a system has a water storage, and rainfall is able to be estimated for that storage, it may also include rainfall on storages.

Outflows

Deliveries

The outflows section of the water balances shows all deliveries or transfers from the water supply system. It shows the type of use, e.g. urban residential, urban non-residential or rural, as well as any transfers to another water system or other water entity.

Losses

Losses in the water supply system water balance represent the amount of water lost after the point of extraction from a river or other water system.

Loss is generally calculated as the difference between the inflows to the system and the known deliveries and outflows.

Depending on the system, the loss may comprise of up to 3 parts:

• reticulation losses represent the loss in the actual reticulation system (the series of pipes connecting customers)
• treatment plant losses represent the loss incurred during the water treatment process
• other system losses typically represent the loss of water from between the point of extraction and the actual reticulation system.

As these types of losses are not consistently recorded or provided by the water corporations, the tables in these accounts show a single line item for system losses.

Where a system has a water storage, and evaporation is able to be estimated for that storage, outflows may also include evaporation from storages.

Water supply system efficiency

Efficiency of the systems are calculated using the formula:

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where Total outflows includes deliveries, water passed to other systems and losses.

Efficiency is a measure of the proportion of the water flowing through each system that is able to be used; i.e. that which is not lost to evaporation or system losses.

The above system efficiency formula is only one of many commonly used in the water industry.

In systems where there is a large balancing item (which implies poor measurement somewhere), the efficiency calculation may be relatively meaningless. In such cases, the system efficiency is presented as n/a (not applicable).

Recycled water

Recycled water is wastewater that has been treated to an appropriate standard at a wastewater treatment plant, then subsequently reused for another purpose. In Victoria, recycled water can be used for a range of non-drinking uses including agriculture, irrigating sports fields and public open spaces, residential, commercial or industrial uses, or for environmental benefit.

 Urban water corporation local reports contain a table and chart showing the volumes of wastewater that is treated and either recycled for various end uses or discharged. These reports also provide a chart that shows the volumes of treated wastewater produced and the component of this that has been recycled for use, over previous years.

Data about treated wastewater availability and recycled water use is collected from water corporations each year by the Essential Services Commission (ESC). The ESC definitions of the various categories are provided below.

Class of water

This is the class (a, b or c) of treated effluent produced at each treatment plant. Water corporations can list more than one effluent class for each treatment plant.

Volume of treated wastewater produced

This item reports the volume of treated wastewater produced by wastewater treatment plants; it is defined as the net volume (ML) of treated sewage produced as effluent from a sewage treatment plant, excluding evaporative losses from the treatment process.

Other inflow

This category has been created by DEECA for the Accounts, not by the ESC. It commonly represents water held in storage from a previous year that is used for customers or discharged.

It may also represent water transferred from another treatment plant, or be used as a balancing item where there is uncertainty in other measured volumes. A comment is generally provided under the table to explain this item.

Supplied to retailers

This item, which applies to Melbourne Water only, reports the volume delivered to retailers.

Recycled for domestic/residential uses*

This use category is defined as recycled water supplied for residential purposes, e.g. via third pipe schemes.

Recycled for municipal uses*

Recycled water used for municipal purposes includes open space, sporting ovals and nature strip irrigation, community gardens, municipal run golf courses, and for supplementing recreational lakes (e.g. recycled water provided to Lake Wendouree).

Recycled for commercial uses*

Recycled water used for commercial purposes includes uses such as firefighting, construction activities such as dust suppression, sand washing, offices, shops, accommodation, and privately owned irrigation (e.g. golf courses, school ovals, race courses, cemeteries).

Recycled for industrial uses*

This reports recycled water used for industrial and manufacturing processes.

Recycled for agricultural uses

Agricultural uses include irrigation, forestry and livestock. This excludes discharge for irrigation or release to land where there is no customer, community group or similar entity using products generated by irrigation

Recycled for beneficial allocation

This describes treated effluent discharged to a waterway for recognised environmental purposes (as prescribed by the Environment Protection Authority [EPA]).

The EPA is developing guidance for the use of recycled water for environmental purposes. Volumes reported under beneficial allocation will ultimately be expected to align with this policy following its development.

Recycled within process

This category describes recycled water used in the water treatment process, e.g. mains flushing, back-flushing filters and other consumption due to operations.

This value is included in the total volume recycled. Often, a volume of water is used within process but not consumed; it is subsequently either used for another purpose or discharged. In these cases, this table reports that volume only once, under its final use or discharge category, to avoid double counting.

Total volume recycled

This column totals the volume (ML) of all treated effluent that is used by either the water corporation, a business supplied by the water corporation, or supplied through a third pipe system for urban reuse. It is the sum of water recycled for domestic/residential, municipal, commercial, industrial, agricultural, beneficial allocation and within process uses.

Total percentage recycled

This is the total volume recycled for use, as a percentage of the volume of treated wastewater produced plus other inflows.

Released to land*

This category reports the volume used for irrigation or released to land for the purpose of disposal where there is no customer, community group or similar entity using products generated by irrigation.

Ocean outfall discharge

This reports disposal of treated effluent to ocean outfalls under an EPA waste discharge licence.

Inland water discharge

This describes disposal of treated effluent to inland water (e.g. a river or stream) under an EPA waste discharge licence.

Other outflow

This category has been created by DEECA for the Accounts, not by the ESC. It commonly represents water transferred to storage to be used or discharged in a subsequent year.

It may also represent water transferred to another treatment plant, or be used as a balancing item where there is uncertainty in other measured volumes. A comment is generally provided under the table to explain this item.