It found that several parties with responsibility for Havelock North's water supply, particularly the Hastings District Council, Drinking Water Assessors (DWAs), and the Hawke's Bay Regional Council failed to adhere to the high levels of care and diligence needed to protect public health, but said these agencies did not directly cause the outbreak.
This week the inquiry resumed to consider any necessary changes to prevent or minimise similar incidents in the future, and will come back with its findings in December this year.
In the meantime, the Hastings District Council, Hawke's Bay Regional Council and Hawke's Bay DHB have taken steps to improve their practices and agreed that the situation today was very different to this time last year.
"There's a greater level of scrutiny on drinking water generally, and the effect of activities on drinking water," said HBRC chief executive James Palmer.
"We're more aware and have more knowledge of the risks and vulnerabilities, and state of the resource."
He said the likelihood of a similar event happening again had decreased due to all the agencies involved being more attuned to the risks, more proactive with risk management and able to manage events more quickly when they arise.
At the time of the outbreak, there was criticism of the authorities' response, particularly the Hastings District Council, but its chief executive Ross McLeod said the inquiry had found it was generally effective overall.
"We do not think we have could have been any faster putting chlorine in - that happened almost immediately.
"If we'd had residual chlorine across the network last year, it's highly likely no-one would have got sick."
Today, Havelock North's water is still being disinfected with chlorine and treated with UV, but if there were to be a contamination of some form, such as chemical, the council was in a better position to respond than it was last year, he said.
Last year it only had a partial Emergency Response Plan but this was now comprehensive and had been found to be effective when E-coli was found in the water at Waimarama and Whirinaki this year.
"We have better information at our disposal around vulnerable groups and have contact details for people and have changed our communications," Mr McLeod said.
The council relied on social and mainstream media last year to keep the community informed but had subsequently added extra tools such as deployable road signage and was rolling out information about the use of mobile loudhailers or "stingers".
The inquiry was also critical of the Hastings District Council's in-house processes that meant the memory of a similar outbreak, at the same location, in 1998 faded.
Mr McLeod said the council now had additional resourcing, had overhauled its inspection and maintenance regime, had improved its internal communications, and had taken expert advice on its water safety plan and procedures.
"We have a far greater focus on water safety - the community should be able to rely on the water supplier complying with the standards and water should be safe to drink."
Both Mr McLeod and Mr Palmer noted that the relationship between the two councils had improved, another area that came in for criticism from the inquiry.
In the ensuing months there had been an increase in mutual respect and empathy about the job each agency had to do, Mr Palmer said.
"We got a clear message from the community that they were not concerned where the responsibilities started and stopped - they wanted to see everyone working together in the community's interest.
"Being precious about responsibilities and jurisdiction is not helpful."
At both senior management and a governance level he said the councils were in regular communication, he added.
"The whole level of engagement has changed and there's goodwill on all sides."
The council's understanding of the aquifer as a water resource for Hastings Havelock North and Napier had grown since last year's events, Mr Palmer said.
"We are learning that rather than being a great underground lake to draw down from it's a system of underwater rivers.
"The water moves through the aquifers much faster than we previously realised, which means contaminants can move through the system more quickly than we had assumed."
He said the way of assessing and managing that risk has changed considerably and that it was being recognised that the Heretaunga water and aquifer systems maybe did not lend themselves to water supply without some form of treatment.
"Our previous assumptions that the source was safe and secure are not as well-founded as we had thought."
In addition, he said that since the outbreak the regional council had better tools and capabilities to assess municipal bores and understand the risks.
The inquiry found that the Hawke's Bay DHB had responded fairly well to the outbreak, but it too had made changes to its systems and accountabilities.
In a submission to the inquiry this week, it said it now took a more active role in monitoring and supporting DWAs, and had clarified and defined the roles and responsibilities of key individuals within the DHB involved in responding to a major transgression event.
Regular operational meetings were being held with water suppliers and it planned to implement quarterly compliance meetings with water suppliers as well as create a means to report historical transgression information for individual water supplies.
