The decision not to declare a state of emergency over the Havelock North water contamination last year aggravated the situation, says the author of an independent report.
John Hamilton, the country's former civil defence director, wrote the report for the Hastings District Council, after more than 5000 people became seriously ill with campylobacter in August.
A sample of Havelock North water tested positive for E coli on a Friday morning. A boil water notice was not issued until 6.30pm that evening and it gained little traction in the wider media.
The report concluded the timing of the notice hindered the message getting out to the community.
Mr Hamilton said it was critical to warn people not to drink the water.
"Had you declared a state of emergency for Havelock North because of the water problem, you might have got a bit more traction from the media, and therefore deeper penetration of the bore water notice."
Mr Hamilton said the report found sections of the community felt they were let down by the council's response.