Water usage per person is calculated by dividing the water abstraction in a year (uptake from aquifers) by the current population (which is estimated between census years).
Selwyn data is calculated for water used within urban schemes only. These urban schemes are Arthurs Pass, Castle Hill, Darfield, Doyleston, Dunsandel, Kirwee, Lake Coleridge, Leeston, Lincoln, Prebbleton, Rakaia Huts, Rolleston, Sheffield/Waddington, Southbridge, Springfield, Springston, Tai Tapu/Otahuna, Taumutu, Upper Selwyn Huts and West Melton.
Water used in Selwyn includes all water that is abstracted. Therefore this includes both residential and commercial/industrial use as well as water leakage.
The Selwyn District Council has nearly completed installing water meters in townships in the district. This programme started in 2015-16 and may have contributed to the decrease in water use in recent years.
Water in Christchurch City is abstracted from the Christchurch-West Melton aquifer. Lyttelton Harbour Basin is also supplied water from this source.
Banks Peninsula is excluded (Diamond Harbour, Governor's Bay and Little River, along with other bays and Akaroa)
Christchurch data includes all water abstraction from groundwater and rivers/streams in Christchurch and Banks Peninsula.
This includes water that is used for commercial or industrial purposes, as well as leakage amount, so there is some data discrepancy.
It is assumed that the amount pumped or abstracted is the amount consumed by the Christchurch Territorial Authority Population.
A proportion of the water abstracted will be used for commercial or industrial purposes or lost due to leakage.