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 6 months old 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 yesterday morning a nitrate level of 11.4 mg/litre was detected.
This was above the maximum acceptable level of 11.3 mg/litre.
"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.
Boiling the water might 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 this morning would confirm the situation had been resolved, he said.
Four water tankers were set to be available last night at Eccles St playground, Hokonui Dr by the fire station, Hamilton St opposite the Oxford St playground and Wentworth St by Talbot St.
The council had notified Taumata Arowai, the national drinking water regulator, and Health New Zealand Te Whatu Ora Southern.
Shoppers were heading to the supermarket in Gore last night to stock up on water. Shelves soon emptied as shoppers swooped on the stocks of bottled water.
High nitrate levels in the drinking water supply of Glenavy, a small town in South Canterbury, have also been a concern for residents.
The issue has led to temporary restrictions on tap water use in Glenavy and prompted the local council to take action to address the problem. — APL
