Although there are no immediate public health concerns, corroding pipes may signal future infrastructure collapses - and it’s not just Christchurch that needs to worry
Under the streets of Christchurch, ageing pipes are leaching asbestos fibres into the water supply.
That’s a finding of a study published today from the University of Otago, prompting experts to call for water pipe replacement to be prioritised by the city's council.
And while the data focused on just the Christchurch water supply, similarly aged infrastructure and the chemical composition of drinking water around the country suggest it may be an issue that other cities will have to face before long.
The study collected water samples from fire hydrants and domestic water taps around the city. The results showed asbestos fibres from 20 of the 20 hydrants sampled and three of the 15 domestic water taps.
Study co-author Dr Sarah Mager, a senior lecturer at the University of Otago’s School of Geography, Te Iho Whenua, said the findings were not cause for public health alarm as the level of asbestos did not exceed international safety standards.
However, it may present an uncertain future for Christchurch’s water supply if the pipes aren’t replaced or upgraded in a timely fashion.
“The study indicates the asbestos in these pipes is degrading and we can detect that,” she said. “They may not be broken yet, but it tells us they are wearing away.”
Part of that is due to the age of the pipes themselves, and part of it’s due to the nature of the water.
“The bulk of the water pipes in New Zealand were laid during the 1960s - they’re already 60 years old. By international standards, that would probably be the end of their life,” she said.
The abundance of soft water in New Zealand, which tends to cause corrosion more quickly, means pipes here may have an even shorter life span.
“Work from Water New Zealand would suggest that actually asbestos in piping in New Zealand may only have a lifespan of up to 40 years,” Mager said. “So what we are looking at is the crisis of them ageing out really quickly and needing to be replaced.”
Soft water contains less calcium and magnesium, so it doesn’t build up a layer of deposit within the pipe. Instead, it starts attacking the pipe.
“Over time, the water erodes the inside of the pipe from the inside out, leaving it thinner and thinner until it breaks,” Mager said. According to the study, asbestos fibres in the water suggest that the pipes are indeed being corroded.
The researchers want to see pipe replacement prioritised by councils across the country, as well as a plan to monitor pipe quality.
Mager said with the pipes out of sight, they tend to fall out of mind.
““It’s infrastructure that’s hidden underground. Just like we don’t check the pipes in our house, we don’t check the pipes out in the road very often,” she said. “So we have this potential hazard that we tend not to replace infrastructure until it stops working, combined with under-investment in the pipes themselves.”
Around 44 percent of Christchurch’s 1814 kilometre-long water mains network was laid in asbestos cement piping, with the oldest sections underneath New Brighton, Hei Hei, Mt Pleasant and Halswell.
Study co-author Michael Knopick, who undertook the work for his University of Otago Masters of Science thesis, said pipe degradation might have also been worsened by the Canterbury earthquakes, as asbestos cement pipes are particularly vulnerable to ground movement.
“We did find quite a significant concentration of asbestos fibres [in liquefaction-struck areas], which would suggest liquefaction [could] have accelerated the deterioration of the pipes,” he said. “Ground acceleration, shaking or vibration can cause them to shear, meaning they can degrade both inside and out.”
Christchurch was chosen as ground zero for the study to see if the earthquakes had sped-up the leaching of the asbestos-fibres.
But although the water mains of Canterbury may have been particularly affected by seismic activity over the past 11 years, degrading asbestos piping is an issue for the rest of the country.
“Most of New Zealand’s water supplies are also characterised as soft, so the problem is pretty transferable to the rest of the country,” Knopick said. According to the study, New Zealand has 9000 kilometres of asbestos piping requiring replacement, at an estimated total cost of NZ$2.2 billion.
The strength and technical superiority of asbestos meant it was the preferred material for pipes around the world in the 20th Century. However, global restrictions on its use began to arise around the 1970s as it became clear the pipes could release asbestos fibres into the water. In this country, asbestos remained the go-to material for water mains until the 1980s.
International studies suggest Europe and North America have around 15 percent of their piping made out of asbestos, while in New Zealand the figure is closer to half.
There is little argument that airborne asbestos is bad for people, but conclusive evidence of it being hazardous or safe to consume in drinking water has yet to be found.
The Environmental Protection Agency in the United States requires safe drinking water to contain no more than 7 million asbestos fibres per litre.
In New Zealand, however, there are no official guidelines or regulations around asbestos in water, while the World Health Organisation says there is insufficient data available worldwide to derive a health-based link to asbestos in drinking water.
However, the authors of the study called for a precautionary approach, due to the topic being under-studied.
“Most studies into the quantity of asbestos in drinking water date back 40 years,” said Mager. “More recent publications suggest precautionary measures should be put in place to limit asbestos fibres in drinking water due to their long latency time.”
