An independent review into a South Wairarapa town's water contamination has said "it was a matter of luck" that the incident was not a repeat of Havelock North.
Just days after the report was released to the public, a boil water notice has been issued again to Martinborough households after "a very low" level of E. Coli bacteria has been detected.
E. Coli was also detected in the Martinborough water supply on the January 30 this year and led to a boil-water notice being in place for 20 days.
An independent report into the first contamination was written by Lutra, an expert water consultancy.
It found the incident "highlighted shortcomings in the design, operation and management of the Martinborough water supply system"
In the town, water is extracted from bores and treated with ultraviolet (UV) radiation, PH corrected and then pumped through the township to reservoir tanks.
There is no chlorination because of the presence of manganese in the water.
The review found the most probable cause of the water contamination was a malfunction at the UV plant, allowing untreated water to enter the supply network.
A power cut occurred on January 23, resulting in a fault in the UV plant that caused the bore water to be pumped to supply without UV treatment.
It continued to be pumped without treatment until the following day, as the equipment remained out of service.
On January 29, a positive E. Coli sample was found at Martinborough School. A boil-water notice was issued three days later.
Multiple Wellington Water emergency bladder tanks were deployed in the town, so residents could have an alternate supply.
The Wairarapa District Health Board said it was not aware of any gastro-related illnesses during the contamination.
In the following weeks, reservoirs were super-chlorinated and fully drained, and the system was flushed. After three consecutive days of testing came back clean, the boil-water notice was lifted on February 21.
The review said the cause of the contamination could not be definitively identified and it was still possible it occurred within the network itself.
The review said the "lack of knowledge of how the plant would respond to power failure is concerning".
"Operators should know how the plant responds to power outages and what is required to protect public health,
"A more vigilant approach should have been taken with the plant being isolated until a detailed examination of the problems and remedial action could be undertaken."
Operators noticed faults with the UV equipment and failed to take immediate action. "This should have led to an immediate plant shutdown as a critical piece of equipment was not functioning correctly."
It laid out 11 potential intervention points that could have prevented the incident occurring, including plant design, only being reliant on one person for plant control and having better operation and maintenance manuals.
The report also said a boil-water notice should have been identified "immediately" after E. Coli was detected.
Dr Jill McKenzie, Regional Public Health's Medical Officer of Health, said an initial investigation by council staff concluded the contamination was isolated to the school, but further investigation found there was a wider problem in the system.
"The Drinking Water Standards of NZ require a water supplier to investigate a positive result and take action to correct any issues and protect public health. A boil-water notice is one action that can be considered.
"Decisions around issuing a boil-water notice depend on the initial thoughts around the likely reason for detecting contamination and what actions can be taken to manage any potential risk."
The investigation also highlighted corrective actions which should be implemented.
On Monday before the new boil-water notice was issued, South Wairarapa mayor Viv Napier said while it was regretful the contamination had happened, it was something they were completely aware of and it was a "catalyst for change."
"It's good we have now got all of this information. We are relieved it didn't cause any increased levels of sickness in the community. We need to now make sure those [issues] that are identified are put into action."
Napier said the council had agreed to move forward installing a manganese removal plant within the next six to 12 months. This would enable full-time chlorination of the water.
The council also held a community meeting on Monday night.
Acting chief executive Jennie Mitchell said about 70 to 80 people attended to talk about the report and what the council was doing to rectify the issues raised.
"The main concern from the community was to ensure that this sort of incident doesn't happen again and to have reassurance from council officers and elected members that we are going to take the action necessary to ensure it doesn't happen again."
Comments from the community on a Facebook post issuing the latest boil-water notice expressed disbelief.
People said it was "unacceptable" and "beyond ridiculous" after being assured at the public meeting procedures were now in place.
The review reiterated the seriousness of the first contamination incident "cannot be overstated".
"It is a matter of luck that this was not another Havelock North or a Walkerton."
Jim Graham, Water New Zealand principal adviser for water quality, agreed and said Martinborough was a reminder that it could have been a "Havelock North type event".
He said although the country had taken some recommendations on board from the Havelock North contamination, there was still a way to go and better education and training in the industry were needed.
Graham was not "particularly surprised" with the outcome of the review.
"We've been saying for quite some time unless there's significant changes to the way we deliver water supply in New Zealand, we are going to have more of these kind of contamination events or worse."
The campylobacter contamination in Havelock North, Hawke's Bay, in August 2016 made 5500 people ill and was linked to the deaths of three people. It led to a government inquiry.
In Walkerton, Canada, 2500 people got ill and seven people died in April 2000 due to a contamination of the water supply.