Perth

30.5 Unaccounted-for difference—water distribution system store

Supporting information

The volume disclosed in the water account statements represents the difference between the measured opening and closing balances of water distribution system assets, after physical inflows and outflows have been applied.

The unaccounted-for difference is calculated according to the table below.

	Account	Volume (ML)
	Opening balance of water distribution system store (as at 1 July 2009)	7,312
add	Total of 19 Water distribution system inflows	356,009
minus	Total of 20 Water distribution system outflows	323,839
minus	Closing balance of water distribution system store (as at 30 June 2010)	7,312
	Unaccounted-for difference	32,170

The unaccounted-for difference is equal to approximately 10% of the inflows and outflows for the water distribution system, and is probably due to errors associated with the following line items:

20.2.2 Leakage from water distribution system to groundwater
20.3.2 Application of water from urban water supply system for irrigation or outdoor use.

Both line item values are not measured and are based on estimated data only.

In addition, water from the urban supply system is consumed for other purposes, such as agricultural, industrial or even household use. These consumption figures are not considered in the National Water Account 2010. Consequently, total outflow from the water distribution system is likely to be underestimated.