Environment Southland is charged with finding what caused the July nitrate spike in Gore’s drinking water and said the process would take some time.
On Friday, July 18, the water sample showed higher nitrate levels than normal — 11.4mg per litre — 0.1mg over the safe limit set by New Zealand’s Drinking Water Standards.
The tap water was then declared drinkable again three days later.
Resource management manager Donna Ferguson said when dealing with discharge into surface water, the source was often immediately visible so could be quickly traced.
With groundwater contamination, as was the case in July, the source was invisible, making the investigation "extremely complex", she said.
Having met with landowners in the area and completed on site assessments, the regional council will now focus on geochemical and geophysical analysis.
"Some of this data exists already but may need to be analysed in a different way," she said.
Councillor Peter McDonald, whose constituency is Hokonui, said during any investigation process it was important not to comment.
These investigations were not cheap to run, he said and took "a lot" of technical and legal resource.
"It would be foolish of me to compromise that by just making assertions or coming up with opinions," he said.
National water regulator Taumata Arowai head of operations Steve Taylor said nitrate levels in drinking water were caused by the contamination of "source water".
Source water includes the surrounding rivers, lakes and aquifers and its protection was critical for safe drinking water, he said.
The protection was the job of Environment Southland as it was the authority who provided consents over the discharge of contaminants into the environment.
A day after Gore’s water was declared drinkable again, the town’s signature brown trout statue and welcome sign were defaced by Greenpeace Aotearoa.
The trout was made to look dead and the altered sign read: "Welcome to Gore, where dirty dairy wrecked the water".
Following this, the organisation called out Gore District Mayor Ben Bell, inviting him to help solve what it called a drinking-water crisis.
The press release also called for the national limit of nitrate levels of 11.3mg per litre in drinking water to be lowered and said levels as low as 1mg per litre had been linked to increased risk of bowel cancer.
"If pregnant people drink water with nitrate levels of 5mg per litre, there is increased risk of preterm birth," the press release said.
Mr Taylor rejected those health claims, citing the World Health Organisation (WHO) and a review by Auckland University research body, the Liggins Institute.
The review in 2021 found no consistent evidence between drinking nitrates and preterm births.
What was a risk was blue baby syndrome, which is possible over the national limit of 11.3mg per litre of water.
While the investigation would take time to conclude, Environment Southland encouraged landowners to test their own bores and domestic water supply.
Their website had more information on nitrates, bore maintenance and testing.
