The general methods used to compile the physical supply and use tables of the water account are relatively straightforward. Data from the WSSS collection operates as a stabilising component, acting as a spine for the compilation. The basic premise behind this decision is that the WSSS collection is a relatively complete census of all water providers – a population who, by necessity, understand the subject matter. The EWES/ EIS are utilised to inform industry splits, excluding Agriculture, and provide detail that is lacking in the WSSS collection instrument. The Agricultural Census and surveys (REACS) fill a similar niche for Agriculture.
With this in mind the following represents a broad outline of how the data feeds into each supply and use water category.
Self-extracted water: the sum of all self-extracted water use sets the supply figure for the environment to the economy.
Distributed and reuse water: derived from the WSSS collection, the vast majority of water is supplied by the Water Supply, Sewerage and Drainage Services industry. EWES water supply estimates set total supply for water providers outside of the Water Supply, Sewerage and Drainage Services industry, while total use by industry is used to allocate these data to states/territories.
Wastewater: currently the WAA does not include estimates for the supply of wastewater to sewerage systems, split by individual industries and households. This is a known data gap that will be explored in future iterations of the WAA. In the interim, the total wastewater supplied is estimated in the account. The total wastewater supply is aligned to the total wastewater received by subdivision 28, sourced from the WSSS collection.
Return flows: formerly referred to as Regulated Discharges in the WAA, return flows estimates are sourced from the WSSS collection (state/territory and national) and EWES (national) surveys, however no data is currently available for return flows from Agriculture and Households. These are known data gaps that will be explored in future iterations of the WAA. Total use by the Waste Collection, Treatment and Disposal Services is used to allocate EWES national estimates to state/territory estimates for the following industries. Mining and manufacturing utilise total self-extracted water in the same way. For Electricity and Gas return flows was matched with self-extracted surface water.