The notice was issued yesterday - after the council advised water services authority Taumata Arowai that nitrate levels in the source water for its Lower Waihao rural supply were above acceptable values.
For several weeks the about 650 households who get their water from the Lower Waihao public water supply have been encouraged to make use of water tanks provided by the council because the rising levels of nitrate in their drinking water.
Yesterday the level rose to the point that the council issued the notice.
High nitrates levels pose an immediate risk to some people's health, particularly pregnant women and babies.
Waimate District Mayor Craig Rowley said the nitrate levels tended to spike after a large rain event.
The council had a similar issue back in 2022 and Rowley said they had been looking at possible solutions.
"We've been looking at a denitrification plant. Unfortunately, none of these things tend to happen quickly by the time you get all the reports and studies and costings and everything else.
"We only get one chance to do this right, and we want to make sure it is the most cost effective and best solution."
Last time it took about two to three months for the nitrate to clear to a safe level, and Rowley expected a similar time frame this time.
Smack in the middle of the affected area is Glenavy school.
Principal Kate Mansfield said they had covered up all the school's drinking fountains, and all children had been asked to bring a water bottle - but that did not always happen.
It was frustrating that little seemed to have improved since the incident two years ago, she said.
"You just feel like it is never-ending really. How many times does this happen at school where we are not allowed to drink our water. It does take a toll. It takes its toll in time, and ensuring all our children do have water at school."
Farming intensification appears to be at blame
University of Canterbury's Ngai Tahu Centre associate professor Tim Chambers said documents showed nitrate levels were low in the Waimate area until about 10 years ago, and had since increased rapidly.
Chambers said the primary source seemed to be from the intensification of farming and changes to irrigation practice.
"The farmers are doing what the consents allow them to do. So the problem really is about whether we think those consents should be allowed given the impact on the land and the water. So it is more of a problem of environmental regulation, than farmers doing something they shouldn't be doing."
Rowley said the council was the meat in the sandwich.
The water services authority, Taumata Arowai, was telling the council that it had breached safe levels, but there was little the Waimate District Council could do to change the situation, he said.
Regulations for farmers were set by the regional council, not the district council, Rowley added.
A statement from the regional council said it was supporting Waimate District Council with the issue.
"This includes encouraging private well owners outside the drinking water scheme to test their water if they use it for drinking. We are committed to taking further steps to improve water quality in this area. As the land use activity regulator, we have boosted our compliance monitoring in the region to ensure potential sources of nitrate are being well-managed."
"This includes on-farm visits to monitor dairy effluent consents in the catchment and checking on permitted activities to ensure they are being carried out within plan limits. We are also working with the local irrigation company on its consenting requirements."
