A visiting Canadian water scientist is at a loss to understand why all New Zealand drinking water is not treated to avoid the risk of illness, he says.
Dr Steve Hrudey - an Emeritus Professor from the University of Alberta - has been in this country to attend the Water New Zealand Conference in Hamilton.
He said water from the ground must be treated because nature does not do the job.
Dr Hrudey studied an outbreak of E coli in the water supply in Walkerton, Ontario in 2000, when seven people died.
He said he was aware of the campylobacterosis outbreak in Havelock North in August last year which affected many people, and said the concept of secure groundwater was a "huge problem".
"It was a shallow well, 11m is not deep. There's ample evidence that there was contamination from time to time. There was a campylobacter back in 1998, so those are a lot of warning signals."
He said to have a major outbreak in 2016 suggested things were not working as well as they should.
Dr Hrudey said the secure groundwater concept was that water could be taken from the ground and delivered to consumers without any treatment, and that somehow nature took care of it. But in Havelock North, the pathogens came from sheep and that was all natural and made people sick.
He said people in countries like New Zealand and Canada, which had an abundance of water, took treatment for granted.
Dr Hrudey compared the use of untreated water supplies to a roll of the dice.
"It is not a question of if somebody will get sick, but a question of when and how many.
"If nothing changes, it will happen again," he said.
He said the answer was simple - treat the water.
"We know how to prevent it. There is simple disinfection technologies available and they are not expensive."
Dr Hrudey said he could not understand the groundswell of opinion against putting chemicals in the water.
"Water is a chemical. We are all chemicals. It is kind of an urban myth that somehow treating water to make it safe is bad. I don't understand that."
The state of water in New Zealand put the country's clean image to some shame, Dr Hrudey said.
He said if tourists were going to be invited, the country needed to be truthful about the safety of the water.
"I am afraid some of the practices I have seen here - and I have seen in places in Canada - the water isn't safe.
"Selling the clean, pristine environmental image along with unsafe water is not reasonable."
Dr Hrudey said there was a responsibility that if water was not treated to international standards, people needed to be told.