Perth

This line item refers to leakage from the irrigation supply system and the public water supply system.

Total leakage from each irrigation district and public water supply region are given below.

Data source

Harvey Water: spreadsheet database.

Water Corporation: Operational Data Storage System andFacilities Mapping System.

Data provider

Harvey Water and Water Corporation.

Method

This line item consists of two components: leakage from the irrigation supply system and leakage from the public water supply system. Both systems are below ground, so it is assumed that any leakage from either system is to groundwater store (not the landscape).

Leakage from the irrigation supply system was estimated as the difference between the water inflow into the system and the volume of water sold or used by the various customers.

Leakage from the public water supply system was calculated by subtracting the metered volume of water consumed from the metered volume of water supplied. However, the water consumed volume was first adjusted to take into account the difference between bulk meter readings (done daily) and customer meter readings (done twice per year for each customer). This is known as the meter lag adjustment. The total volume of water consumed comprises the sum of allowances for unmetered authorised consumption, unauthorised consumption, and customer meter under-registration. The losses are equivalent to 0.5%, 0.1% and 2% of these three allowances, respectively. These figures are based on the Infrastructure Leakage Index for Perth and Mandurah.

Uncertainty

Ungraded.

Approximations, assumptions, caveats/limitations

• It is assumed that the leakage from the irrigation supply system is the difference between the volume released from the reservoirs and what is sold to the customers. However, water not used by the customer that drains into a downstream surface water channel (return flow) is not metered and is not included in this calculation. Therefore, it is likely that this leakage value is an overestimate.
• For both systems, there is no differentiation between leakage to the landscape and leakage to the groundwater system, it is simply assumed, in this case, that all losses go to the groundwater store.
• It is assumed that most of the losses in the irrigation supply system are attributed to metering error, rather than actual leakage from the system.