Hunua Ranges

There are five earth dams in the Hunua Ranges: Mangatangi, Upper Mangatawhiri, Cosseys, Wairoa and Hays Creek. They were constructed between 1951 and 1977. Each dam is constructed on the headwaters of the river it is named after, apart from Cosseys, which is on the headwater of the Wairoa River.
They supply around 57% of Auckland's bulk water.

	Mangatangi Dam Completed 1977 Lake area: 185 hectares Capacity: 35.3 million cubic metres
	Mangatawhiri Dam Completed 1965 Lake area: 128.5 hectares Capacity: 16.2 million cubic metres
	Cosseys Dam Completed 1955 Lake area: 123 hectares Capacity: 14.03 million cubic metres
	Wairoa Dam Completed: 1975 Lake area: 98 hectares Capacity: 11.6 million cubic metres
	Hays Creek Dam Completed 1967 Lake area: 18.2 hectares capacity: 1.1 million cubic metres

Each dam has an intake valve tower that is used to feed required quantities of water into the pipeline that connects to the Ardmore Treatment Station. This raw water mixes with raw water coming in from Hunua dam before it is treated.

Ardmore station has a sophisticated computerised monitoring system that automates much of the production of up to 318,000 tonnes of drinking water a day.

After being treated, the water is stored on site in two large buildings and piped from there into reservoirs nearer the city. The pipes it initially travels in are as big as 1.9 metres in diameter.