Contaminated water from the Tukituki River could have infected the Havelock North water supply, says a former GNS Science hydrogeologist.
The presence of E coli indicates that other, more harmful bacteria - such as campylobacter - could be infecting a water supply.
An estimated 4100 people have suffered from gastric illness following the contamination of the water supply and some 500 were confirmed as due to campylobacter. Several people were hospitalised, and a coroner is looking at whether the death of an 89-year-old woman, who had contracted campylobacter, was from other underlying causes or was connected to the infection.
Hydrogeologist Gil Zemansky said a report produced by GNS Science and the Hawke's Bay Regional Council in 1997 showed water from the Tukituki River charged the Havelock North aquifer about 1m per second.
Dr Zemansky said it would normally take about 200 days for water from the river to reach the contaminated bore sites.
But he said the clay soil all through the area had deep cracks in it because of a winter drought.
"When you have dry conditions, dry and hot conditions, clay basically desiccates and shrinks and you can get cracks in the clay that can provide pathways for that type of situation, where water could go quickly down there if you have an overland flow."
Dr Zemansky said a major storm that occurred just before the water supply was poisoned could have sent contaminated water from the river through cracks in the clay directly into the aquifer.
Hawke's Bay Regional Council chair Fenton Wilson did not deny that some of the measures were very low, but speaking to Checkpoint with John Campbell, he said that did not mean it was the cause of the illness.
"It's a long bow to draw that set of data to the issue that's happened in Havelock North and, as I say, speculation is not helpful at this time."
"What I can say though categorically is the Tukituki River ... has clear bore samples between the Brookvale site and the Tukituki River itself.
"It is extremely unlikely that E coli came from the Tukituki River."
Hastings District Mayor Lawrence Yule said he welcomed any advice on how the poisoning of the Havelock North water supply could have occurred because the council had no idea.
He said a helicopter flew around the catchment yesterday trying to spot the source of contamination from the air such as new holes in the ground.
"To see actually whether there's anything suspicious, holes, anything that looks like it could have been part of this, because as I've previously said it remains a mystery."
The council has already said the contamination was most likely to have come from cattle, sheep or deer faeces.
Mr Yule said the council was working as hard as possible to find the source of the contamination so it could be prevented from happening in the future.
Claims crisis experts kept away from media
Meanwhile, a prominent scientist is questioning why council specialists are not fronting to help explain the water crisis.
Shaun Hendy recently published a book about scientists talking in the media called Silencing Science.
He said regional and district council scientists were working on the crisis but were missing in action when it came to informing the public.
But Mr Yule said his council had not been deliberately keeping scientists working on the crisis away from the media.
He said scientists were busy investigating the causes of the disaster and the best thing was to let the experts get on with the job.