Wastewater from the mushroom farm, which may contain bacteria, could have become "hydraulically connected" to the groundwater system.
The report recommended the council assess whether the changes to the landscape could adversely affect groundwater, and that it do a "human health risk assessment".
It further recommended an expanded testing programme to better identify the source of contamination.
Te Mata Mushrooms owner Michael Whittaker said the report investigates an event three years ago and commissioned 18 months later.
"We are really disappointed it is being released in draft form, with people drawing conclusions in the heat of the moment," he said.
"In our view it doesn't draw conclusions."
Hastings Mayor Lawrence Yule also said the report was inconclusive but its findings would be included in a wider investigation of the current outbreak. Yesterday Health Minister Jonathan Coleman confirmed there would be a Government-initiated independent Inquiry into the contamination issue
A test on which animal the campylobacter came from is due today.