The majority of experts giving evidence at the Havelock North water contamination inquiry say drinking water needs to be treated to avoid contamination.
The group of five were asked to give their opinion on a range of issues at the second stage of the inquiry, which began in the Hastings District Court today.
All but one agreed that treating water was fundamental to stopping outbreaks.
"The debate shouldn't be whether we should be treating drinking water but why we shouldn't be," water treatment engineer Iain Rabbitts said.
Drinking water specialist Jim Graham said it wasn't always necessary to treat water and risks could be managed through other means, adding that treatment alone wasn't enough.
Mr Graham said there needs to be an emphasis on ensuring those overseeing water management were properly trained and that strong water safety plans were in place.
Drinking water expert Dr Daniel Deere said treating water was often a more simple and cheaper often.
The panel also discussed whether the community should be part of the decision making process when deciding to chlorinate drinking water supply.
Mr Graham said the community should be consulted and, if they had the money to do so, they should be allowed to explore other options. He also said mandated treatment could breach the Treaty of Waitangi as some Maori were against the idea.
Mr Rabbitts said chlorine was the "biggest advancement of the 20th Century" and had saved more lives than seat belts and penicillin.
The hearing also heard that there are up 34,000 cases of water borne gastro illnesses recorded in New Zealand each year.
Some of the panel said that figure could be higher.
Stage two of the inquiry has a national focus and is looking at what changes could be made to water management and how to prevent another outbreak.
In August last year 5500 people became ill with gastro after Havelock North's water supply was contaminated. The first stage of the inquiry determined the source of the contamination was sheep faeces getting into the water supply via a pond.
Stage two of the inquiry will continue until the end of the week, with recommendations due in December.