Pahiatua residents will have to continue boiling their water until at least tomorrow, despite a clear sample being recorded yesterday.
E coli was found in the Tararua district town's water supply late last week, and a chlorinator has been up and running since mid-afternoon on Friday.
It follows a widespread outbreak of campylobacter in Havelock North, which was thought to have affected more than 5200 people.
Tararua mayor Roly Ellis told Morning Report they got a clear sample at Pahiatua yesterday afternoon but needed two more days of clear samples before the boil notice could be lifted.
"We do have a bore that is between 65 and 90m down that we take from, so we're going a lot further down than what is done in Havelock, and we're quite surprised it has happened, to be honest."
Mr Ellis said an investigation into how the water became contaminated would begin today.
Meanwhile, businesses in Havelock North have started applying for assistance from a $200,000 fund set up by the Hastings District Council and the government to help the town get back on its feet.
Firms can apply for cash grants, interest-free loans and penalty-free rates deferment.
Chris Morris, who owns the Pipi Cafe, said people started putting in their applications on Friday.
"Everyone's just handing their numbers in, it's a couple of pages about how the trade has been for you this year as compared to last year, which is exactly what you'd expect them to assess, really. And they're got a panel that will go through, and the answer will just spit out, 'well you can pay your rates a bit later', or some businesses will really be affected a lot more than others."
The boil-water notice issued for Havelock North three weeks ago was withdrawn on Saturday.