Asbestos in New Zealand’s Urban Water Mains

Asbestos in New Zealand’s Urban Water Mains: The Impacts of Aging Infrastructure.

Asbestos cement was a common construction material for water pipes during the twentieth century. Research conducted by the University of Otago, investigated whether aging asbestos cement pipes, used for potable water distribution, are releasing asbestos fibres into New Zealand’s municipal drinking water supplies. It found that 789 km of asbestos cement pressure pipe remains actively in use in the Christchurch water supply network.

Key outcomes from the study are outlined below:

Most of New Zealand’s source waters are soft (low calcium carbonate), making asbestos cement piping vulnerable to internal corrosion. Therefore, local predictive models of pipe lifespan range from 20–60 years rather than the 70 that is usual for piped networks overseas.

Drinking water sampling was targeted to pipes installed before the 1980’s (1930-1970’s) and results found abundant evidence of fibres being released from pipes installed in this period. 

20/20 hydrant samples returned positive results for the presence of short chrysotile asbestos fibres (> 0.5 µm) with an average concentration of 6.2 million fibres per litre (MFL). Short asbestos fibers (SAF) had the highest concentrations in drinking water samples, with five hydrant samples exceeding 5 MFL, including the highest concentration measured at 56 MFL.

19/20 hydrant samples showed long asbestos fibres (>10 µm), with an average concentration 0.9 MFL. Asbestos fibres were detected in hydrant samples across all water supply zones (excluding Kainga). The highest concentrations of fibres (as SAF) that exceeded 7 MFL were detected across Christchurch, and there is no discernable clustering at this scale of sampling. Additionally, 15 domestic water taps were also sampled and asbestos fibres were detected at 3 properties, averaging 0.2 MFL (>10 µm) and 3.5 MFL (>0.5 µm). There was no obvious spatial clustering to the positive detections in household water taps. 

From this study it is evident that asbestos cement pipes are corroded by the soft, highly aggressive municipal water supply, with mean lifetime corrosion rates of 0.20 mm a-1. The mains water supply in Christchurch is therefore contaminated with (predominantly short >0.5 µm) asbestos fibres from decaying asbestos cement pipes.

Research publicly available from: IWA- Water Supply Journal