UPDATED 7.34PM Hastings mayor Lawrence Yule has apologised to a crowd of hundreds gathered tonight in Havelock North.

Around 450 people are at the first of two public meetings being held in the township where about 4,700 residents became sick from contaminated drinking water.

LISTEN ABOVE: Newstalk ZB reporter Annette Hilton speaks with Larry Williams from tonight's meeting

Lawrence Yule said this has been the largest water borne outbreak of disease in New Zealand's history.

"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."

Mr Yule said they still don't know the source of the bug, and will leave no stone unturned to find it.

SEE ALSO: Meetings for Havelock North community to provide answers

Environmental scientist Stephen Swabey from the Hawke's Bay Regional Council told the crowd that they're focusing on the area directly surrounding the two infected bores.

"We're looking at potential connections between the Mangateretere Stream itself, which flows quite close to the bore network. We're also examining whether paddocks around the water supply bores might have a close connection."

Bernie Bowden from Forest and Bird Society told the expert panel the oversupply of dairy cows is at the root cause of the outbreak.

"Our society has been calling for many, many years for our rivers and our streams to be cleaned up, but nobody's taken a damn bit of notice about it. We're in trouble, and we're in deep trouble."

The crowd has been informed the boil water notice should be lifted in two days time.

Hawke's Bay District Health Board CEO Dr Kevin Snee said they need to have the utmost confidence in the water supply being safe, especially from other water borne bugs.

"I think from a health perspective, we're very much through the worst of it now. We're not seeing many cases of campylobacter. We don't think any of the other contaminants are in the water supply."