Hastings Mayor Lawrence Yule has again apologised to Havelock North residents over the "misery" caused by the water contamination crisis.
However, he says the source of the outbreak of a gastric illness that has hit 5100 of the town's 14,000 residents is still unknown.
"Simply put, this has been the largest water-borne disease outbreak in New Zealand's history," he told hundreds who turned out of a public meeting at the Riverbend Bible Church on Tuesday night.
"The Hastings District Council is charged with supplying residents with safe drinking water and we have failed to do this.
"On behalf of the councillors and the staff we apologise for this and deeply regret the inconvenience, the misery and financial implications of this contamination."
Earlier this month the town's water supply bores were contaminated with campylobacter and E.Coli but initial tests failed to show it.
"As we stand here tonight we do not currently know the source of this contamination," Mr Lawrence said, adding it was possible the bores may have failed to remain sealed or the aquifer itself could be contaminated.
However, Transparent Hawke's Bay chair Megan Rose says this isn't enough to restore trust in the council - and she wants more information.
"A regional council shouldn't be investigating itself," she said on Paul Henry.
"This inquiry should be a judicial inquiry or a public inquiry. The Government inquiry doesn't require it to be tabled in Parliament. We need to have the public involved in this, and we need to have accountability around how those findings are delivered."
Newshub.
