He also revealed that the Hastings District Council was working on a water plan for all Hastings so Brookevale Rd bores can be turned off in future and Havelock North would still have water.
Mr Yule said the would be chlorination of water "for the foreseeable future". He said he is "ruling nothing out for the cause".
Hastings District Council CEO Ross McLeod said the council was working closely with the Hawke's Bay Regional Council to look for the cause.
The Hawke's Bay District Health Board acting officer of health William Rainger said a small number of notified cryptosporidium and giardia cases was not unusual for this time of year.
Because campylobacter was recently found in Havelock North water there were concerns the other two organisms could be in the water, so a boil-water notice was issued.
He said a "dramatic increase" in the two diseases would be expected if they were in the water, which had not happened.
Skin problems from chlorination was a "rare occurrence" and surveillance for other waterborne organisms would continue into next week probably, Dr Rainger said.
Mr McLeod said there was a tradeoff between chlorination and security of water supply.
He said there have been incursions of aquifer water in past due to backflow accidents and there was a need for community discussion on the tradeoff between water purity and water safety risk.
Mr Yule also produced a copy of a press release one of his councillors, Wayne Bradshaw, sent to TV3 accusing the council of knowing about the bug on Wednesday, August 10.
He said he "will not tolerate" false information" and there had been no attempt to clarify or respond. He also criticised another councillor, Simon Nixon, for "misinformation".
A boil water notice remains in place for Havelock North until further notice.
