20.3 Leakage to groundwater
This line item volume (336 ML) represents the leakage from the irrigation water supply system into groundwater aquifers within the Perth region during the 2011–12 year.
Leakage from the irrigation water 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.
Assumptions, limitations, caveats and approximations
It is assumed that the leakage from the irrigation water supply system is the difference between the volume released from the storages 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.
There is no differentiation between leakage to the landscape and leakage to the groundwater store, 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 water supply system are attributed to metering error rather than actual leakage from the system.