National Water Account 2016

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Key findings

Climate and water

Water Accounting Statements

Supporting information

Region description

Reference information

Perth: Governance

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 2016, such as extreme precipitation and significant water rights purchases. This information is publicly available elsewhere.
• Asset changes for water stores (surface water and groundwater) 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:

        – Unregulated river
        – Regulated river
        – Lakes and wetlands
        – Water table aquifer
        – Underlying aquifer

        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.

Robert Argent

Assistant Director, Water Information Services

Bureau of Meteorology

27 April 2017

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 (Department of Water)
• 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 2015 to 30 June 2016.

Transactions between water assets and water liabilities within the region (e.g., between the surface water store and the groundwater store) are not reported in the water accounting statements because they do not affect the region's total water assets and water liabilities.

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 or the urban utilities 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. 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 the Water rights, entitlements, allocations and restrictions 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 rivers, lakes and wetlands, and groundwater aquifers (see Water assets note in 'Supporting information').

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

The volume of one change to water assets identified in the region was not reported in the water accounting statements but replaced by a dash ('–') as it 'failed the recognition criteria' specified in the Australian Water Accounting Standard 1, because it could not be quantified in a way that is complete, neutral, and free from material error.

The volume that failed the recognition criteria describes the river and floodplain losses (see Surface water store note in 'Supporting information').

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.

The following comparative year volumes in the water accounting statements were removed or restated from the 2015 Account due to a change in presentation:

• Supply system (urban water)
• Wastewater
• Recycled water
• Supply system (irrigation scheme). 

These items relate to water assets within the urban water system and the irrigation scheme and represent water held in the distribution pipes and channels, and service reservoirs. They are no longer considered water assets in the region as this water is needed for operation of the system/scheme and no direct benefit is derived. The changes are summarised in Table N1.

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

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