Water in Flaxmere and Hastings tested positive for E. coli on Saturday afternoon, the Hastings District Council has confirmed.
The water supply remains safe to drink after chlorination was introduced on Thursday, says Hastings City Council chief executive Ross McLeod.
He says the results are "totally unexpected and unusual in Hastings" and further samples have been sent for testing.
Mr McLeod says the results are not cause for alarm because chlorination should be enough to treat the low levels detected.
"We have consistently had clear results in Hastings for a very long time, so we are double-checking," he says.
"We reiterate that the water is safe for drinking because of the chlorine. It does not need boiling before drinking."
Further test results are expected back by Sunday afternoon.
The number of people hospitalised by the campylobacter outbreak in Havelock North is falling while the hunt for its source and an investigation into the death of an elderly women continue.
In an update on Saturday, Hawke's Bay District Health Board chief executive Kevin Snee said the outbreak was "coming under control".
The number of confirmed cases of campylobacter is 476, up slightly from 472 on Friday. The number of people in hospital is 10, down from 17 on Friday, and no one is now in intensive care.
The DHB continues to recommend all water be boiled and chlorination of the water supply is continuing.
An estimated 4100 people in the Hawke's Bay township have been affected by gastric illness as a result of the contamination, the source of which remains unclear.
Hastings' mayor Lawrence Yule and the DHB will meet with the family of Jean Sparksman, 89, who died one week ago, four days after becoming ill from campylobacter.
Coroner Peter Ryan has said a post-mortem examination showed Mrs Sparksman also had other underlying health problems, which will be assessed in his inquiry into her death.
Massey University senior lecturer in Ecology Mike Joy told The Nation on Saturday there is a wider issue at stake - New Zealand has the highest rates of gastro diseases that come from animals in the developed world.
"And, so we may never find the cause of this, but we can go to places like Canterbury and we can look at the huge increases that have happened."
There is intensive farming and lots of water taken from shallow bores in Canterbury, he said.
The Government has been "out of the room" on the issue of intensification of agriculture, he said.
A government investigation into the contamination in Havelock North and its aftermath will be formulated next week, according to Health Minister Jonathan Coleman.
On Friday an interim scientific analysis by Institute of Environmental Science and Research indicated contamination from cattle, sheep and deer may have been present in Havelock North's water supply, which is not normally treated with chlorine.
The testing suggested a ruminant source such as cattle, sheep or deer.
"These genotypes are not consistent with a poultry source. Isolates from the bore sample are most closely related to wildfowl isolates," ESR said.
Campylobacter in very rare cases can cause complications including reactive arthritis or the neurological Guillain-Barre syndrome.
Doctors were being briefed by the health board on how to spot and treat such conditions as a precaution.
Newshub. / NZN