The Tararua District Council is seeking outside advice after another positive E.coli test has been returned for Pahiatua's water supply.
District mayor Roly Ellis said although people must continue to boil their water, the contamination is not in the town's water reticulation (pipe) system.
"This is so frustrating, especially after the high hopes we held after Sunday's clear test," Mr Ellis said.
"I went down to Pahiatua yesterday with Dave Watson, our utilities manager, and can assure people the Pahiatua bore is properly fenced, sealed and secure.
It's very odd that we had a completely clear sample on Sunday, but another positive one yesterday, so that's why we're seeking outside help, just to confirm the actions we are taking are correct.