Onehunga Water Treatment Plant increases production as part of drought response

Pumps at the Onehunga Water Treatment Plant
Pumps at the Onehunga Water Treatment Plant.

Onehunga Water Treatment Plant is getting a four million litre a day (MLD) boost as part of our drought response work.
The plant is in Spring St and draws water from an underground aquifer to supply Onehunga residents with 20MLD. By the end of May, a $2 million upgrade project will be completed, taking production to more than 24MLD. New pumps and pipes will increase the amount of water drawn from the aquifer. New filtration units and operational procedures will boost the plant’s ability to process the water.
All this means more water not just for Onehunga residents but also for the central city, which can receive water from the Onehunga plant when aquifer levels are high. It will also be the major second water treatment plant upgrade to be completed in the last three months, following the opening of the new Papakura Water Treatment Plant earlier this month.
Infrastructure project manager Giorgos Lourmas says the additional water will be an important boost to Auckland’s overall supply: “The Onehunga aquifer and treatment plant is one of Auckland’s oldest water supplies. The water it provides is as important today as it was when it first came into operation at the turn of the last century.
Some of the buildings are very old and working in small spaces has presented an extra challenge for the 25 or so engineers and filtration experts working on the project.”
The upgrades were given the go-ahead in June last year and construction teams began work in late November.  The plant has five pumps: three lsrger and two smaller ones. One of the larger pumps was replaced. The new model can draw more than 460,000 litres of water per hour.
The upgrades don’t just mean more production capacity. They also make the plant more resilient and sustainable.
Onehunga is our shallowest aquifer and lies within basalt and basanite lava. It resembles a underground river, in that it rises and falls according to rainfall. In winter, the aquifer can be just 10m below ground level and is visible through the inlet point. This compares to other aquifers within the Auckland region, such as Warkworth, which is more than 180m deep.
Water restrictions were introduced in May last year, following Auckland’s record-breaking drought. The period between 1 November 2019- 20 April 2020 was the driest six-month period on record across our catchments in the Hūnua and Waitākere ranges.
Aucklanders have listened to our calls to reduce water use and more than 10 billion litres of water have been saved since restrictions began.
February’s water demand target is 511MLD. On Monday (15 February), Aucklanders used just 412MLD. Onehunga residents have also reduced their water usage to 7MLD (January 2021 average), as compared to 9MLD in the same period last year.