It's possible Hastings and Havelock North water supplies will be permanently chlorinated.

Chlorine is being used to treat the campylobacter contamination in Havelock North, which has affected around 4500 people.

It's the first time ever Hastings water has been treated with chlorine.

Hastings District Council chief executive Ross McLeod says there will always be a risk for future contaminations in untreated water.

"We will need to have a community discussion about that trade off around pure aquifer water versus the risks that come with not treating."

Mayor Lawrence Yule said it could become an election issue.

"There is a community preference here around non-chlorinated water but we need to understand that that in itself brings some risk."

The Hawke's Bay District Health Board's downplaying public concerns about the increase of skin conditions due to water chlorination.

Acting Medical Officer of Health Dr William Rainger said it's rare for chlorine to affect people's skin.

"In very, very small numbers of cases people with existing skin conditions, like eczema, might have that made worse by chlorine."

Dr Rainger said the dose of chlorine in the drinking water is much lower than what is in swimming pools.

A bigger spotlight is now also being put on the testing regime for drinking water around New Zealand.

Mr Yule said the government-lead in-depth investigation will examine the testing of drinking water.

"Is the testing regime robust enough? Does something need to be changed? How could this happen because at the moment it is unexplainable what has happened. We had a negative test using a probably accredited system."

The boil water notice is likely to remain in Havelock North until possibly next week.