This water is used to supply the Christchurch urban area, Lyttelton, Diamond Harbour and Governors Bay.
Christchurch's underground aquifers mean residents continue to enjoy an untreated water supply from natural underground reservoirs.
Water is taken from many wells around the city, sunk down into the aquifers. There are 55 locations around the city where water is pumped into the pipe network. At each of these extraction sites there is at least one, and sometimes up to six, wells. These wells are typically 200mm and 300mm in diameter and are drilled down to depths ranging from 22–220 metres.
There are five layers of confined aquifers, with approximately 25% of Christchurch’s water supply being sourced from the shallowest aquifer. A programme is underway in the northwest of the city to replace some shallow wells with deeper wells, and once this is complete only 15% of the city's water will come from the shallowest aquifer. The water in these confined aquifers is under pressure, giving rise to artesian wells that in some locations flow freely at the surface. This reduces pumping costs and, due to the high quality of the groundwater, treatment is not required meaning that this water has low processing costs and is inexpensive to produce compared with other cities in New Zealand.
In Christchurch, water is delivered into water mains by electrically driven pumps keeping the mains pressurised and charged. The pressure forces water out of the tap when you turn on a tap in your house.
Where reservoirs or large tanks are sited on hill areas, water pressure is maintained by continually supplying water to the level of the reservoir. In areas where there are no nearby hills to put tanks on, pumps are kept running to ensure a continuous water pressure 24 hours a day.
Although Christchurch appears flat, there is actually a significant difference in land elevation from the east to the west of the city. Up to five pressure zones are needed, depending on the height of residential development. In addition, there is also a small public water supply at Brooklands and Kainga.
The water supply network is controlled from a central control room. As the pressure in the system falls and rises around the district, pumps are switched on and off by a combination of automatic and manual controls.
A vast network of pipes cover all urban parts of the city. This underground infrastructure spans from Belfast in the north to the hill suburbs in the south, and from Templeton in the west to Taylors Mistake in the east. Over 1,700 kilometres of main pipes are laid - enough pipes to run from Christchurch to Whangarei. The total length of underground pipework, including submains, is 3,300 kilometres.
This network of pipes ensures that when a section of pipe has to be isolated for replacement or repairs, the number of households affected by stopped water supply is minimal. The main distribution pipes are made from fibrolite, PVC, polyethylene and cast iron. The pipes distribute all of the water and provide water for Council-maintained fire hydrants on the main pipes.