The first half of a billion-dollar pipe that will drastically reduce wastewater overflows in the Auckland isthmus is now in operation. 

As I biked south, I thought about all the poo sloshing beneath my wheels. Tubes of it disgorging from U-bends, into wastewater pipes laid under our streets that become progressively wider, flowing downhill all the way to the Māngere wastewater treatment plant where I was heading. 

Sometimes, as many residents of New Zealand cities know, the wastewater doesn’t make it to the municipal facility. Thanks to ageing infrastructure designed for smaller populations, it spills out into the ocean instead, creating a serious health hazard, and meaning people can’t go swimming after heavy rain. 

First proposed in 2004, the Central Interceptor pipe is expected to reduce at least 80% of the wastewater overflows that pollute Auckland’s beaches. Built to handle most of the city’s waste water, it’s intended to last for at least a century as Aotearoa’s biggest city continues to grow. My route, skirting around the back of Mount Albert, over Hillsborough and crossing the water to Māngere, was roughly the same as that of the tunnel being drilled to house the giant pipe, but with a better view. The pipe will end at Point Erin, just underneath the city end of Auckland’s Harbour Bridge: the tunnel boring machine is currently somewhere under Jervois Quay in Herne Bay, and the pipe will be operational by 2026. 

But while the further end of the interceptor pipe is still under construction, the first half is ready to go now. When I reached the wastewater treatment plant, which is next to Ambury Regional Park, there was a steady trickle of people, half in hi-vis jumpsuits and half in business casual, trickling towards the “dry well”: a 40-metre-deep hole in the ground where the Central Interceptor terminates. 

This is just one small, new part of the plant, smelling like concrete mingled with an earthy, not unpleasant, whiff of waste. At the event to celebrate the southern half of the pipe being turned on, there was a clear message that the Central Interceptor was meant to be the pride of Auckland. As an audience waited for Auckland mayor Wayne Brown (stuck in traffic, an engineer behind me whispered), video screens around the well played tingly chords over time lapses of the Sky Tower and Harbour Bridge and people shuffled to the edge to take photos of the big hole. 

Unlike these monuments, the pipe, by its nature, will remain invisible to most people, yet all Aucklanders will benefit from it.

“As an engineer, this is a huge feat,” said Wayne Brown when he finally arrived, his voice echoing through the dry well, which was not designed for acoustics. Brown, unlike the besuited Watercare leaders and dignitaries perched on a small platform beside him, was wearing shorts and a Blues T-shirt. Someone handed him a walkie talkie, and he gave the order to start the pump: everyone clapped as the sound of humming drifted from the bright blue pipes below. 

Simon Watts, the minister for local government, had a different takeaway. “Everyone in Auckland, including ratepayers, will benefit,” he said of the Central Interceptor, praising particularly the way Watercare found a “commonsense balance-sheet solution… that will mean lower rates and charges”. The pipe has cost $1.5bn to build, and while a budget increase was needed, it was in line with inflation over the construction period.

I asked Watts what councils with less capital to invest in major infrastructure could learn from the construction. “We need to make sure that councils are financially sustainable,” he said. “Regional CCOs [council-controlled organisations] could provide some certainty in funding and financing water services, and protect the pressure on rates.”

There are big questions about how to manage water infrastructure, especially with the risks of climate change making extreme rainfall that could cause wastewater overflows more likely. “How do you share the costs when these events occur? How do you make sure that information is flowing between the different entities and the government?” Watts says. The government is apparently “working on a framework” under the Local Water Done Well programme to get some answers to these questions, but Watts insisted that the solutions would look nothing like the previous Labour government’s maligned Three Waters programme.  

At the bottom of the dry well, Watercare’s programme delivery officer Shayne Cunis looked relieved that the big test was over; the ceremonial toilet had been flushed and the pumps were ready to operate. “If it starts raining, then more pumps will turn on,” he said, gesturing to the big concrete wall. The other side of the dry pit is the “wet well” which can fill up with wastewater. “The system is completely automated; if the levels of water go up, the pumps speed up too.” 

The grittiness of solid waste, kind of like sand, can wear down the parts of the pumps, which all need to be replaceable, said Hamish Spence, a project engineer for the Central Interceptor. Each pump can handle 1,200 litres per second, which means the system as a whole can process as much as 7,800 litres of wastewater if it needs to operate at full capacity, in a situation like the Auckland Anniversary floods. “I find it a bit hard to picture – imagine 21,000 Coke cans in a second,” Spence said. The pipe ends beneath sea level, with the tunnel created with a very slight slope so wastewater will flow downhill to the treatment plant. 

Having the southern end of the Central Interceptor operating is a start, but most of the environmental benefits to clean the isthmus’s water will come when the second half is finished. When the formalities were over, workers, media and guests alike took the elevator back to the surface to enjoy some refreshments, several holding heart-shaped Valentine’s balloons that had been released when Brown and Watts flushed a demonstration toilet after their speeches. “It was interesting to see something that is usually just for engineers – I didn’t know a wastewater plant could be so exciting,” said a woman in flowy blue trousers. “I can see why the engineers are excited,” agreed her companion. At the bottom of the big hole behind them, spectators gone, the pumps kept humming.