Four international water experts believe all of New Zealand鈥檚 drinking water should be treated.
The comments have come during the second stage of hearings into Havelock North鈥檚 water contamination crisis.
This week marks a year since three people died and more than 5000 people became sick with campylobacter.
Dr Colin Fricker said it is critical that all drinking water be treated.
"If you have no treatment then your only barrier is source protection. If that fails, as it did in this case, then you are laying yourself wide open to problems."
The Government Inquiry into safe drinking water also heard that the public need to be made more aware of the risks of untreated water.
Water scientist Dr Daniel Deere says people should be given more information about unsafe drinking water.
"There shouldn't be a sense of fear or panic among the public, just a sense of awareness that there are such things as background endemic disease from water."
There are at least 34,000 cases of illness from drinking water every year.
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