Shane Lynch's inquiry said the crisis cost the company £7.5m.

"This does not reflect the considerable costs that many individual households and commercial premises incurred," the report said.

It found there was a failure of the company's executive leadership and that communication with customers was inefficient. At the height of the crisis, a million people phoned the NI Water helpline.

The report also highlighted that NIW's emergency planning for the winter freeze was deficient.

At the time it was suggested that the network was too old to cope with the unprecedented weather, however the report found that the water mains in Northern Ireland are "relatively new" compared with other parts of the UK and performed as well as could be expected.

It said: "There is no need for an immediate change in mains infrastructure investment levels. However, there is a need for some further capital investment focused on improved flexibility of mains operation and better monitoring.

"There is also a need to think about the future investment needs arising from water resources management and a changing climate."

“Many of the steps recommended within this report have already been put in place and we will press forward to implement those remaining as quickly as possible.

NIW’s interim Chief Executive, Trevor Haslett

The company's chief executive Lawrence MacKenzie resigned earlier this year after facing widespread criticism over his handling of the crisis.

But the 121-page document said that frontline operational staff did perform well during the winter freeze.

Welcoming the publication of the report, Regional Development Minister Conor Murphy said: "NI Water's response fell far short of what was needed."

"The emergency resulted in a significant failure to deliver the most basic of services to people and NI Water has to learn lessons from this especially in relation to communication with customers during such incidents."

The Utility Regulator specifically investigated the role of NI Water in the crisis, while the Office of the First and Deputy First Minister also commissioned a separate inquiry into the Department of Regional Development's role.

Commenting on the findings about his own Department, Mr Murphy said: "The report has concluded that I was fully engaged for the entire period in seeking to deal with the situation and performed all my roles and responsibilities effectively, in a manner fully consistent with the governance requirements.

"I was further reassured that my senior officials were found to have discharged their roles and responsibilities effectively throughout the freeze thaw event."

Antoinette McKeown, Chief Executive of the Consumer Council, said: "Consumers want lessons to be learned from previous failings to ensure that such a crisis is never repeated. They want concrete assurances from the Executive that changes to improve NI Water's preparation and response to supply outages, regardless of the cause, will be made with immediate effect. "

Northern Ireland Water's interim Chief Executive, Trevor Haslett, said he was fully committed to taking forward all the recommendations proposed by the Utility Regulator.

"We in Northern Ireland Water fully accept that many lessons need to be learnt from what was an exceptionally difficult time for many of our customers.

"The past year has been a difficult time for this organisation for a variety of reasons and we have been placed under the utmost scrutiny."

"I am convinced that working together with our various stakeholders and our dedicated workforce, we can provide our customers with a service that we can all be proud of."