Cattle and other four-legged farm animals may be behind the gastro outbreak that has made thousands sick and may have contributed to an elderly woman's death.
Poultry manure may now be out of the frame.
An interim scientific analysis indicates contamination from cattle, sheep and deer may have been present in Havelock North's water supply, which in normal times is not disinfected with chlorine.
It is estimated that more than 4000 people in the Hawke's Bay town have suffered symptoms such as vomiting, diarrhoea, headaches, muscle pain and fever from drinking the town's water when it was contaminated with campylobacter bacteria.
Hawke's Bay medical officer of health Dr Nick Jones said animal faeces might have caused the contamination.