Exactly how toxic the water flowing into the Hauraki Gulf used during the SkyCity firefight is will be revealed in test results due to be released tomorrow.

At the height of the fire that broke out on Tuesday last week in the under-construction New Zealand International Convention Centre firefighters were using 250 litres of water a second.

Watercare has confirmed to the Herald a total of 27 million litres was used to extinguish the blaze, or about one per cent of the city's total water usage in a week.

During the fire fight some of the water, mixed with contaminants from burning building materials, ran into the city's stormwater network and into the Hauraki Gulf.

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The New Zealand International Convention Centre, three days after its roof caught fire. Photo / Niwa
The New Zealand International Convention Centre, three days after its roof caught fire. Photo / Niwa

As much as eight million litres of it also accumulated in the basement of the convention centre where it rose to 1.5m and submerged about 100 cars.

Most of the water had since been pumped out, and Fire and Emergency said today the remaining sludge would be removed separately to avoid it entering the wastewater system.

Initially that water was being pumped into the stormwater system and into the harbour, as there were concerns about potential contaminants damaging the wastewater network's biological reactors.

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However, preliminary test results by Watercare confirmed the wastewater network could handle the contaminated water, and last Thursday evening the pumps switched over.

An Auckland Council spokeswoman on Thursday said they were still awaiting the full test results to see exactly how contaminated the water was, but they should be released by Friday.

Concerns were raised at the time about the contaminated water being pumped straight into the Hauraki Gulf.

Moana Tamaariki-Pohe, deputy chair of the Hauraki Gulf Forum set up to advocate for the marine environment, said it could be "potentially devastating" for sensitive ecosystems.

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"The Gulf is already stressed, and adding all of this contamination is hugely devastating. Our stormwater system needs to be prepared to handle this so it doesn't happen again."

The SkyCity fire seen from Devonport. There are concerns about impacts of the contaminated water used in the fire fight on the Hauraki Gulf. Photo / Michael Craig
The SkyCity fire seen from Devonport. There are concerns about impacts of the contaminated water used in the fire fight on the Hauraki Gulf. Photo / Michael Craig

A Watercare spokeswoman said water from the convention centre fire was being discharged into the wastewater network via a manhole in Nelson St at a rate of 20-25 litres per second.

It was carried by 400mm diameter wastewater pipes to Māngere Wastewater Treatment Plant to be treated.

There had been no adverse effect on the biological reactors there, she said.