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Ageing underground pipes around New Zealand are leaching asbestos fibres into city water supplies, a University of Otago study has found.

While there are no immediate concerns for public health, the study authors are calling for councils to prioritise their pipe replacement programmes.

Study co-author and School of Geography senior lecturer Dr Sarah Mager, of Dunedin, said drinking water samples from asbestos cement pipes in 35 locations across Christchurch, laid between the 1930s and 1960s, were studied.

It found "abundant evidence" of both short and long asbestos fibre release in all Christchurch water supply zones (excluding the modern development at Kainga).

Asbestos cement was commonly used for water pipes worldwide in the 20th century due to its strength and thermal and chemical resistance, and the pipes had been widely used in New Zealand water mains, including Dunedin’s, until the 1980s.

In the 1970s it became clear these pipes, when damaged, could release asbestos fibres into water supplies, prompting global restrictions on their use.

Dr Mager said the findings were significant, but were not cause for public health alarm.

“While there is no regulatory threshold for asbestos fibre limits in New Zealand drinking water, and no maximum acceptable value of ingested asbestos from water yet internationally identified, the amounts detected in this study do not exceed levels of concern for human health.

However, there was insufficient data worldwide to derive a health-based link to asbestos in drinking water, Dr Mager said.

"Most studies into the quantity of asbestos in drinking water date back 40 years.

"More recent publications suggest precautionary measures should be put in place to limit asbestos fibres in drinking water due to their long latency time."

Study co-author Michael Knopick, who undertook the study for his University of Otago master of science thesis, said Christchurch’s asbestos cement pipes were being corroded by the soft and highly aggressive municipal water supply, which was low in dissolved calcium and magnesium.

"The outer surface of the pipes is also vulnerable to decay, especially in conditions where there are high groundwater tables, which is what happens with prolonged liquefaction."

Dr Mager said many of these pipes had reached the end of their life.

"Some are up to 80 years old and therefore 20 to 30 years overdue for replacement.

"We believe authorities should prioritise replacing pipes over 50 years old to reduce the risk of water-carried asbestos release, and to mitigate any potential risk of asbestos from ingested contaminated water sources."

New Zealand had 9000km of asbestos piping requiring replacement, at an estimated total cost of $2.2 billion, she said.

No cause for alarm - council manager

Christchurch City Council's acting head of Three Waters Tim Drennan said people should not be alarmed by the study's findings.

"The levels of asbestos found were incredibly low. Although the study focused on Christchurch, nearly every water supply network in New Zealand has some asbestos pipe work," he said.

"Internationally there is no consistent evidence to suggest that ingested asbestos is hazardous - a fact the authors of the study acknowledge."

Drennan said 190km of piping had already been replaced and the council was progressively working through the rest, based on their condition.

"Around 66 percent of breakages in the past 12 months have been asbestos pipes, which means that the asbestos pipes have been prioritised for replacement over the coming years anyway, just due to their condition," he said.

"Between now and 2045 the vast majority will be fully replaced."

New Zealand has 9000km of asbestos piping that needs to be replaced at an estimated cost of $2.2 billion.

The research article was published by the International Water Association's Water Supply Journal.

- additional reporting by RNZ

john.lewis@odt.co.nz