A boil water notice remains in place for the Manawatū township of Foxton Beach, because of possible E coli contamination.
It came into force before midday on Thursday.
The bacteria was found at two sample sites: Holben Parade Park and Manawatū Marine Boating Club.
Horowhenua District Council issued the notice as a precaution and said it did not believe the water network was contaminated, but more testing was being done.
Residents should boil water for drinking, preparing food and brushing teeth, and infant formula should be boiled before use.
E coli can cause stomach cramps, nausea, vomiting and diarrhoea, but boiling made water made it safe, the council said.
"I'd like to thank the Foxton Beach community for their patience and understanding," Horowhenua District Council acting chief executive Brent Harvey said.
"I understand this is inconvenient, and for some people alarming. However to assure public safety, it is important that we keep the boil water notice in place until we have clear test results showing that the water is safe to drink."
Harvey said as soon as the water is cleared as safe to drink, the news will be posted on the council's website and Facebook page.