A boil notice has been issued for residents who take their water from the Hastings District Esk water supply.
Tests taken yesterday showed E. coli in the water supply, affecting about 80 properties in the area of Esk Ridge and Kanuka Cliffs.
Hastings Mayor Lawrence Yule said the E. coli was found in the reticulation not the actual bore.
"The bore had a clear test but the pipes had a positive test and at this stage we are not sure what the cause is which is why we have issued the boil notice."
Hastings District Council asset manager Craig Thew said residents in the area should boil the water before using it for drinking, cleaning teeth, making ice, washing dishes and preparing food, until further notice.
"Boiling water in an electric kettle kills bacteria and other organisms in it. The kettle only needs to be boiled once for one minute. Please follow this advice to avoid gastroenteritis [diarrhoea and vomiting] and other serious illnesses."
"If you are using a saucepan to boil the water up, then heating it to a rolling boil will be sufficient, before taking it off the heat and allowing to cool naturally."
Chairman of the Esk Hill Residents Society Gary Pollock who lives on Esk View Rd said he had sent an email out to all of the members advising them of the boil notice.
He was not initially notified by council but was alerted by Eskdale School and media.
"I wanted to make sure all of the members knew and I also made calls to families with young children as I wanted everyone to be safe especially being around dinner time where you're preparing food."
Mr Pollock said clean water was an essential requirement and if it had the potential to affect people's health it needed to be rectified immediately.
Medical Officer of Health Dr Nicholas Jones said health officials were not yet aware of any reported sickness from the area but asked people to contact their family doctor or the Healthline on 0800 611 116 if they felt sick with diarrhoea or vomiting.
Council staff are working to discover the source of the contamination in the supply and will work to keep the residents informed of their progress.
Mr Yule advised people to continue boiling the water for the next two days to be safe until a cause was identified and they were advised otherwise.
The system has since been flushed and the water chlorinated.
This latest positive E. coli test adds to the district's water issues coming just two months after Waimarama was issued with a boil water notice.
The notice was lifted one week later after chlorine was added to the supply and all test results came back clear.