National Water Account 2018

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Key findings

Climate and water

Water Accounting Statements

Supporting information

Region description

Reference information

Perth: Governance

• Accountability statement
• Water accounting policies
• Reconciliations

Accountability Statement

1. This water accounting report has been prepared and presented in accordance with the Australian Water Accounting Standard 1, with the following exceptions:

• No assurance statement was prepared because the standard for, and practice of, assurance of water accounting reports are currently not available.
• Notes on the quantification approaches and levels of uncertainty are incomplete because the knowledge base is often inadequate.
• No information is disclosed about material events that occurred after 30 June 2018, such as extreme precipitation and significant water rights purchases. This information is publicly available elsewhere.
• Asset changes for water stores have been included in the Statement of Changes in Water Assets and Water Liabilities, without a corresponding water store asset volume being included in the Statement of Water Assets and Water Liabilities for the following line items: Aquifers. This is because water store flows could be quantified but storage volumes for these items could not
• Groundwater outflows at the coast have been offset (reporting the net result of outflows and inflows) due to limitations in the available quantification approach (Inter-region coastal outflow).
• The volumes of water assets and water liabilities including the volumes of changes to water assets and water liabilities that failed the recognition criteria were reported in the water accounting statements with dashes ('–') in order to highlight data and knowledge gaps that may affect the water accounting statement balances.

2. The report has been compiled from the best data available, as detailed in the water accounting statement notes, in the time available to compile it from a number of sources. The Bureau of Meteorology takes a nationally-consistent approach to report preparation and presentation, but for a few line items there may be local data of higher quality that were not used.

3. All significant and specific interpretations of the Australian Water Accounting Standard 1 for the purpose of preparing this report are explained in the 'Water accounting policies' note. The Bureau of Meteorology is responsible for these interpretations.

Matthew Coulton

a/General Manager Water

Bureau of Meteorology

28 February 2019

Water accounting policies

Introduction

The information presented in the Perth region water accounting report is based on collaboration between the Bureau of Meteorology and:

• the Western Australian Department of Water and Environmental Regulation (Department of Water and Environmenal Regulation)
• the Water Corporation of Western Australia (the Water Corporation)
• Harvey Water.

This report has been prepared using an accrual basis of water accounting, with the exception of the physical water flow information. The water attribute being quantified is volume, and the unit of account is megalitres (ML). Where a reported volume is negative, it is shown in brackets. The applicable reporting period is from 1 July 2017 to 30 June 2018.

The volumes of water transfers to and from lakes and wetlands are included within the volumes of water transfers to and from the water table aquifer. In effect, this means that lakes and wetlands are considered to be a part of the groundwater store in the Statement of Changes in Water Assets and Water Liabilities and the Statement of Water Flows because they are where the water table is exposed at the surface.

Recognition of water assets and water liabilities

Only water that is held or managed by the State licensing authority, the urban utilities or the irrigation scheme, and from which a future probable benefit can be derived by the region's stakeholders is defined as a water asset.

Water liabilities are constituted by present commitments to supply water, the discharge of which is expected to result in a probable decrease of the region's water assets or a probable increase in another water commitment to supply water. 

Provided its volume can be quantified in a way that is complete, neutral, and free from material error, the volume of the water asset or water liability is recognised in the Statement of Water Assets and Water Liabilities.

Water held in storages that has already been abstracted from the entitlement system is deemed not to be part of the region (regardless of the storage's size or connection to the system). This is because the attendant water right has already been exercised.

Recognition of changes in water assets and water liabilities

The increases and decreases to the reported water assets and water liabilities consist of changes that can be quantified in a way that is complete, neutral, and free from material error. These volumes are presented in the Statement of Changes in Water Assets and Water Liabilities and the Statement of Water Flows.

Precipitation and evaporation are recognised only in relation to the surfaces of open storage volumes and rivers. They do not represent all precipitation and evaporation within the region (notably, these processes occurring from the landscape are not captured).

That portion of runoff that flows into the surface water store (storages and rivers) is quantified and recognised in the Statement of Changes in Water Assets and Water Liabilities. This runoff includes precipitation captured in the catchment less evaporation and infiltration, and is recorded as runoff to surface water.

Allocations announced on regulated entitlements have been recognised as increases in water liabilities. Note that the definition of regulated or unregulated entitlements for the purpose of the National Water Account (refer to 'Glossary') may be different to the meaning applied by the jurisdiction. Please refer to Water rights and use for more information on the allocations.

Water assets and water liabilities that fail the recognition criteria

The volumes of several water assets identified in the Perth region were not reported in the water accounting statements but replaced by dashes ('–') as they 'failed the recognition criteria' specified in the Australian Water Accounting Standard 1, because:

• they could not be quantified in a way that is complete, neutral, and free from material error; and/or
• they were unlikely to provide a future benefit to the region or the region's stakeholders.

Water assets that failed the recognition criteria include groundwater aquifers (see Water assets note in 'Supporting information').

Changes to water assets and water liabilities that fail the recognition criteria

There are no items to report under this category for the 2018 Account.

Restatement of comparative year information

In accordance with the Australian Water Accounting Standard 1, comparative year volumes must be restated in the statements if there is a prior period error or a change in line item presentation. Comparative year volumes are not required to be restated if there is a change in scope or methodology, or subsequent data availability for the quantification of a line item.

Between-store flows

In the 2013–2017 Accounts, transactions between water assets and water liabilities within the region (e.g. between the surface water store and the groundwater store) were not reported in the water accounting statements. In the 2018 account, however, these between-store transactions were included as they provide a better understanding of the water movement that occurs at each water store or system. Comparative year volumes for these transactions are also reported.

Region boundary change

Comparative year volumes related to the irrigation scheme were restated from the 2013, 2014, 2015 and 2016 Accounts due to a region boundary change. The Perth region boundary was extended for the purpose of incorporating the full extent of the Harvey Water Irrigation Area, including the Wellington Reservoir. The comparative year items restated in the 2018 Account include:

• Storages (surface water)
• *Irrigation scheme claims: surface water (asset)
• *Irrigation scheme claims: surface water (asset increase)
• *Irrigation scheme claims: surface water (asset decrease)
• *Allocation remaining: irrigation scheme
• Delivery: inter-region (surface water)
• *Adjustment and forfeiture: irrigation
• Delivery: irrigation scheme
• Leakage: landscape (irrigation scheme)
• *Allocation: irrigation scheme

*These items are between-store claims that were not reported in the statements prior to the 2018 Account but did appear in the notes.

Urban water system

Comparative year volumes related to urban water assets were restated from the 2013, 2014 and 2015 Accounts due to a change in presentation. Urban water assets, which represent water held in pipes and channels, and service reservoirs, were no longer considered as water assets in the region as this water is needed for operation of the system and no direct benefit is derived.

Comparative year volumes relating to some urban flow volumes were also restated from the 2013, 2014, 2015 and 2016 Accounts due to a change in presentation. This change in presentation separated supply system discharges to reservoirs from those to rivers as a riparian release. Previously, these flows were classified as a single flow from the urban system. In addition, groundwater replenishment from the urban system as either discharge to groundwater or managed aquifer recharge was reclassified as a single aquifer recharge item. The comparative year items restated in the 2018 Account include:

• Supply system discharge: reservoirs
• Supply system discharge: riparian release
• Managed aquifer recharge

As these are between-store flows, they were not previously reported in the statements but did appear in the notes prior to the 2018 Account.

Irrigation scheme

Comparative year volumes related to irrigation scheme water assets were restated from the 2013, 2014 and 2015 Accounts due to a change in presentation. Irrigation scheme water assets, which represent water held in pipes and channels, were no longer considered as water assets in the region as this water is needed for operation of the system and no direct benefit is derived.

Groundwater store

Comparative year volumes for the change in groundwater storage were restated from the 2013, 2014, 2015, 2016 and 2017 Accounts due to a change in presentation. The change in presentation separated the actual change in aquifer storage from the unaccounted-for difference volume in the water accounting statements. Previously, unaccounted-for difference included changes in aquifer storage.

Comparative year volumes for groundwater inter-region coastal outflow were restated from the 2014, 2015 and 2016 Accounts due to a calculation error.

Unaccounted-for difference

The unaccounted-for difference for 2013, 2014, 2015, 2016 and 2017 Accounts was also restated as a result of the changes described above.

Reconciliations

Introduction

The following reconciliation tables verify:

• how the region’s closing water storage in the Statement of Water Flows reconciles to the total water assets reported in the Statement of Water Assets and Water Liabilities
• how the water accounting region’s change in water storage in the Statement of Flows reconciles to the change in net water assets reported in the Statement of Changes in Water Assets and Water Liabilities.

Closing water storage to total water assets

*between-store claims

Net change in water storage to the change in net water assets

*between-store claims