He said the council's knowledge and awareness of the aquifer and the risks fell below the required standards, including the state of numerous uncapped or disused bores in the area.
Mr Stevens said the regional council also failed to monitor compliance with the conditions of permits granted to Hastings District Council to use the bores.
He then listed the Hastings District Council failings including the fact it did not embrace or implement a high standard of care required as a drinking water provider, particularly in light of the fact it had dealt with a similar outbreak in 1998.
The district council's failings applied especially to its mid-level managers, Mr Stevens said, who delegated tasks but did not adequately supervise and ensure their implementation.
He also noted the district council did not maintain the bores adequately and was slow to get a report on borehead security.
The Hawke's Bay District Health Board was said to have handled the situation well.
Earlier he said none of their faults, omissions or breach of standards directly caused the campylobacter outbreak but they did contribute.
"It's been accepted by those responsible for the failings that greater diligence and co-operation is needed for a higher standard of care and it needs to be in place soon."
The panel was originally due to report back on March 31, but due to delays at the start of the process and the amount of material to be covered it postponed releasing its findings until today.
Mr Stevens iterated that it was highly likely that contaminated run-off from a sheep paddock after heavy rain on August 5 and 6 entered the Mangateretere pond near Brookvale Bore 1 and caused the outbreak.
Water from the pond entered the aquifer and flowed across to Bore 1 where it was pumped into the reticulation, he said.
Another possibility was that the contamination occurred when water from the neighbouring paddocks entered roadside drains adjacent to bores 1 and 2 and then entered the bore chambers.
If enough of that water had got in it may have overtopped the boreheads, the seals were loose and the water may have travelled down the cables and into the water supply.
"This is considered much less likely than the pond theory," he said.
The outbreak was also linked to the deaths of three elderly people, caused Havelock North businesses to suffer financially, cost local agencies nearly $4m and sparked national concern about the safety of untreated water.
Since the outbreak the Hastings and Havelock North water supplies have been chlorinated, including at Brookvale Bore 3 which was re-commissioned to augment water supply to the village during the summer months.