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The review for the Ministry of Health praises the timeliness of the decision to tell residents of Waikouaiti, Karitane and Hawksbury to stop drinking tap water, from February 2.
The review’s authors said blood testing of residents to assess whether there might have been long-term exposure to lead was set up quickly and communication by Public Health South about risk was excellent.
However, they highlighted the "extreme delay" in bringing laboratory results to the attention of health authorities.
This had hindered the timeliness of the health response.
Much of that seemed to result from the Dunedin City Council’s original purpose of the testing, which was to assess corrosion within the network of pipes for asset management.
Routine drinking water compliance was handled separately.
Report authors Dr Heather Uwins-England and Dr Jill McKenzie commented this was unfortunate and the council said the problem had since been rectified.
Lack of timely access to specialist advice was identified as another frustration.
Authorities had their first indication of contamination as early as August last year, when the result came back from a July 31 sample.
The council did not pass on the results of other samples in breach of the lead level considered acceptable until January 8.
One delay of several weeks occurred because an email was sent to an inbox not monitored while a council staff member was on leave.
A separate review by the Dunedin City Council is pending and the health report poses questions for the council investigation to explore.
Some results were not initially notified by the council and Public Health South did not find out it was responding to a series of lead spikes until January 22.
The council has been unable to find the source or sources of the contamination, although it has been replacing pipes in Waikouaiti to eliminate a likely candidate.
Dunedin Mayor Aaron Hawkins said many of the review’s recommendations had already been dealt with.
“We know this has been an incredibly difficult period for residents in Waikouaiti, Karitane and Hawksbury Village, and we are doing everything we can to support them and restore their normal water supply as soon as possible.”
Council chief executive Sandy Graham said it had changed the way it reported lead results detected above the allowable limit and how it communicated those results.
It also bought machinery from Belgium that would test for lead every 20 minutes as it entered Waikouaiti’s water treatment plant.
“We’ve made other improvements too, such as bringing forward pipe replacement work, and we’re planning an upgrade of the Waikouaiti water treatment plant.”
The latest water test results have continued to come back either clear of any sign of lead or within acceptable limits.
Reinstating permanent water supplies could be two months away, Ms Graham said.
Director-general of health Dr Ashley Bloomfield said the overall finding of the ministry’s rapid review was the public health risk assessment and response were timely and appropriate, "particularly around informing the community and undertaking lead screening".
Public meetings in Waikouaiti were well received and blood tests helped determine residents’ overall exposure to lead, he said.
“Less than 40 people were found to have lead exposure above notifiable levels and, on further assessment, many were found to be higher than normal due to other environmental factors."
Associate Minister of Health Dr Ayesha Verrall said the actions of health agencies resulted in reduced risk to public health.
The report made several recommendations to reduce the chances of a similar scare in future.
"They include improvements to several areas in the current and proposed regulatory framework for drinking water, such as better reporting by water suppliers and a review of the process for public health units to access expert advice," Dr Verrall said.
The report also raised concerns about New Zealand’s plumbing standards.