Minute Molluscs Discovered in Water Supply

New Zealand’s common native freshwater snail Potamopyrgus antipodarum (New Zealand Mud Snail) was discovered this week in the Hanmer Springs water supply.

A precautionary boil water notice was put in place while we sought to identify it and to find out if its presence posed any health risks to our consumers.

NIWA provided identification yesterday, and this was confirmed by New Zealand’s most eminent malacologist, Dr Bruce Marshall, who also provided reassurance that Potamopyrgus antipodarum is not a vector for any known human condition, and “is harmless”.

After confirmation from Community and Public Health, we were able to lift the boil water notice today.

Extensive investigations were undertaken throughout Hanmer Springs yesterday to find how widespread the snails may have become. The conclusion was that they had colonized reasonably extensively and had probably been in the system for many years.

Potamopyrgus antipodarum are tiny – most of those found were just 2-4mm. They were only discovered during routine flushing when our water officer spotted one as they took a sample. Sampling is not usually carried out during flushing – it is normally a process carried at the treatment station and a couple of places on the reticulation.

Consumers are unlikely to have encountered the minute molluscs because there are filters at the meters going into each property.

Key messages:

• The presence of Potamopyrgus antipodarum poses no risk to health

• The precautionary boil water notice has been removed

• The chlorination levels in the system have been increased moderately (still well within acceptable health tolerances) to enhance biofilm removal and interrupt any further breeding

• Flushing of the system will intensify

• Supply testing is carried out regularly and there is no presence of E.coli in the system

• If you have reduced water pressure please contact us so that we can check your filters

ENDS

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