Watercare operates 14 water supply reservoirs, five of them located northwest of Auckland in the Waitākere Ranges, two near Helensville, four to the southeast in the Hūnua Ranges, and one east of Papakura. In combination the reservoirs are capable of storing over 100 million cubic metres of water.
- The dams supply about 80 per cent of Auckland’s water.
- Because the dams are located at high elevations, water flows easily to the city by gravity.
- Earlier dams in the Waitākeres were made of concrete. After World War II they were built with earth and rock.
- The Hūnua and Waitākere ranges receive about 1.8 metres of rain annually – about 50 per cent more than central Auckland.
Dams in the Hūnua Ranges
The water is piped to Ardmore Water Treatment Plant. It is then stored and carried through pipes, which are up to 1.9 metres in diameter, into reservoirs nearer the city.
- 5 earth dams
- Supply: About 60 per cent of Auckland’s water
- Built: 1951-1977
- Location: Headwaters of the Hūnua River. Cosseys Dam is on the headwater of the Wairoa River.
Dams in the Waitākere Ranges
Raw water from these dams is piped to treatment plants in Huia, Titirangi and Swanson.
- 5 dams, 3 concrete, 2 earth
- Supply: about 20 per cent of Auckland's water.
- Built: 1907-1971
- Each dam is named after the stream that feeds into its reservoir.