Water from underground aquifers is used to supply the Christchurch urban area, Lyttelton, Diamond Harbour and Governors Bay.
The Council has a consent from the regional council, Environment Canterbury, to take water from wells within the city, sunk down into the aquifers. There are 56 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 200 millimetres or 300 millimetres in diameter and are drilled down to depths ranging from 22 to 220 metres.
There are five layers of confined aquifers, with about 15 per cent of Christchurch’s water sourced from the shallowest aquifer. The water in these confined aquifers is under pressure, reducing pumping costs and also giving rise to artesian wells that in some locations flow freely at the surface.
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 water storage reservoirs 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. 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 covers 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. More than 1,700 kilometres of main pipes are laid – enough pipes to run from Christchurch to the Chatham Islands and back again. 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.