20 years of Tantragee Water Treatment Plant

Nelson City Council is this week marking 20 years of the Tantragee Water Treatment Plant, which has been providing top-quality potable water to Nelson residents, businesses and visitors since 2004.

Prior to the commissioning of the state-of-the-art treatment plant, the city was subjected to water boil notices when water was deemed too dirty to drink which was considered unacceptable for a growing city with a hospital, substantial tourism and national and international food processing industries.

The previous “treatment” system relied on a simple mesh to screen the water, later adding chlorine before it was released to the city. The new technology uses world cutting microfiltration membranes – panels covered with hundreds of spaghetti-like strands with microscopic holes in them. Water is sucked in and blown through these membranes repeatedly, each time sucking up clean water and blowing out dirty water. Dirty water pumped into settlement lagoons where sediment is allowed to settle out and water again been sent to the plant for treatment, a unique aspect of the Tantragee Water Treatment Plant.

Nelson Mayor Nick Smith paid tribute to previous councils for standing firm despite criticism of the multimillion-dollar cost of building the water treatment plant, which has been providing Nelson with some of the best-quality water in the country for two decades.  

“This investment of $26 million (it would cost $100 million today) is why Nelson is so well positioned in the national debate about water services and why we have not seen the outbreak of waterborne diseases that have occurred elsewhere. It has provided our city with about 20 billion litres of safe drinking water without a glitch over the past 20 years.” 

In August 2004, Council completed the build of the plant, which treats water from both the Roding and Maitai catchments. 

In the two decades since the plant has been operational, there have been no boil notices issued as a direct result of the treatment plant. 

The current facility can process an additional one billion litres of previously unusable water per year from the Maitai Dam, meaning it can treat seven billion litres of water per year. That’s the equivalent of 2,800 Olympic-sized swimming pools, or 46.6 million bathtubs. 

The Tantragee water plant was built after almost a decade of investigations into various methods for water treatment. 

Initial plans had two treatment plants, one in Marsden Valley at the end of the Roding raw water supply and one in the Maitai below the Dam. Following a public tender and innovative thinking from a consortium, the decision was made that one plant would be built as this provided benefits in reduced maintenance, fewer materials, fewer staff and would be a better option in the long term.  

The location chosen by the consortium required heavy excavation of the rocky hillside.  

Twenty years ago, NCC’s Deputy Chief Executive/Group Infrastructure Manager Alec Louverdis was the Project Engineer tasked with overseeing the project. 

“It’s one thing to build a plant, it’s another to deliver the water through the city.  

“Provisions needed to be made to bring the water from the Roding catchment across to the Tantragee site, treat the water and send it back to the Stoke catchment across some undulating terrain. This was complex and required a lot of discussion and negotiation with multiple private landowners by the consortium. 

“Of all the years I have been at Council, this is one of the projects of which I am most proud,” he says. 

A consortium of Fulton Hogan/Montgomery Watson was finally awarded the tender under a design, build operate tender. 

“It’s not a typical approach, but it meant we had skin in the game, extra incentive to make sure it would work,” says Fulton Hogan Project Manager at the time and now Fulton Hogan Regional Manager Gavin Stobie.  

“It wasn’t just a theoretical design, we brought in the guys that would operate the plant so we could include their input in the functionality of the design. 

“This has become a poster plant for Fulton Hogan, an example we refer back to. It’s been a privilege to be a part of the journey from design to build and to be here celebrating it 20 years later.” 

Louverdis says the only challenge encountered by the new plant since it opened was in the 2022 August floods.  

“Alongside everything else that happened that day, the pipeline feeding raw water to the treatment plant from the Maitai was destroyed by a landslide, the generator at the treatment plant malfunctioned and the area had a power failure. Fortuitously council did have a backup pipeline buried in the road between the dam and the treatment plant and was able to continue to supply uninterrupted water to the city. This second line was put in by the council of the day after the only supply line was damaged by a severe wind event in 2008. That extra resilience proved its worth.  

“I am confident we have created something that will outlast us, providing clean drinking water to Nelson for generations to come,” he says.