Watercare starts upgrading Auckland’s oldest watermains in Onehunga

Auckland’s oldest watermains are getting a much-needed upgrade to enhance network resilience and ultimately improve water discolouration.

This week, Watercare started work to replace Onehunga’s cast iron watermains, which were installed between 1910 and 1935, making them the oldest in the city.

The $6m package of work started yesterday <20 April> with our key contractor, Kerry Drainage and Civil, beginning working on a section of Arthur Street and the corner of Symonds Street, laying new polyethylene pipes.

This package includes two work areas and is expected to be completed in in the first half of 2027.

The work is part of Watercare’s $13.8 billion, 10-year infrastructure programme, with around half of that investment dedicated to replacing or upgrading existing assets.

It is the start of a long-term work programme to ultimately renew all the cast iron watermains in the Onehunga water supply zone within 15 years.

Watercare project manager Sean McHenry says the cast iron pipes have slowly corroded inside over time, causing discoloured water.

“Over the years, these pipes have developed reddish-brown, iron-oxide nodules called tubercles on the inside due to corrosion. The water is safe to drink, but the corrosion affects its appearance.

“The new pipes will be made from polyethylene which will provide an extended asset life and improve water discolouration by eliminating corrosion issues. They will be installed using either open trenching or directional drilling depending on ground conditions.”

He says that improving the water discolouration will take time.

“Because of the age of the wider network of pipes in the area, discoloured water may keep appearing while we do this work. The water is still safe to drink – this is a long-standing aesthetic issue.”

In addition to its regular water quality monitoring programme, Watercare will carry out increased water quality monitoring throughout the watermains renewal programme to provide extra assurance to the community that their water supply is safe to drink.

Traffic management will be in place in stages throughout the works.

“We appreciate that this work will be disruptive for the community, and we sincerely appreciate people’s patience as we do these much-needed renewals,” says McHenry.