Gore District Council is sending water tankers out on the streets to supply free drinking water.
Elevated nitrate poses a health risk to people, particularly to infants under six months and pregnant women.
The council's general manager of critical services Jason Domigan said in a statement a monthly sample showed a nitrate increase in the water supply.
When the water was tested again this morning a nitrate level of 11.4 mg/L was detected.
This was above the maximum acceptable level of 11.3 mg/L.
“While the health risk to the general population from this minor exceedance is low, as a precaution, we advise all households to avoid using tap water for drinking purposes until further notice.
"This includes for drinking, food preparation, and brushing teeth,” he said.
Water could still be used for washing although care should be taken when bathing young children.
Animals had a higher tolerance to nitrate so owners could decide if they wanted to give their pets water from the tap, he said.
Boiling the water may increase concentrations of nitrates, he said.
The council was pumping water from the Mataura River into the Coopers Well bore field to dilute the nitrate concentration, he said.
It was hoped that testing tomorrow morning would confirm that the situation had been resolved, he said.
Four water tankers would be available at: Eccles Street playground, Hokonui Drive by the Fire Station, Hamilton Street opposite Oxford St playground and Wentworth Street by Talbot Street.
TThe council had notified Taumata Arowai, the national drinking water regulator, and the Southern District Health Board.
