The town’s mayor said Greenpeace’s testing was less accurate than the council’s, a claim Greenpeace said was "not true".
Greenpeace held a nitrate contamination testing event, where the public could bring in a sample of their tap water from home to be tested for free.
Gore has been the focus of Greenpeace’s freshwater campaign since its tap water was declared undrinkable from July 18-22 when its nitrate levels spiked 0.1mg over the 11.3mg per litre (mg/L) national limit.
Environment Southland (ES) were charged with finding the cause of the nitrate spike, and told the Otago Daily Times yesterday they had concluded their investigation — with no clear answer.
On Thursday, Gore District Mayor Ben Bell told the Otago Daily Times Greenpeace’s testing method was less accurate than the council’s.
Greenpeace used an optical spectrometer which he said had a "significant" margin of error of 2mg/L, compared to the council’s lab testing.
At the event, Greenpeace spokesman Will Appelbe said that margin of error was incorrect.
The spectrometer was standard for nitrate testing in the field, and was "robust".
They had collected the largest data set of its kind in the country on nitrate contamination, some of which had been used in published research at the University of Otago.
Because of that, their testing method was externally reviewed by Earth Sciences New Zealand.
A print-out of a recent review available at the event showed at a nitrate level of 11mg/L, the testing had an error margin of 0.17mg.
But that is not the only point where the mayor and Greenpeace disagreed.
Mr Appelbe said the main source of nitrate contamination was land use, specifically intensive dairy farming and the overuse of synthetic nitrogen fertiliser.
While Mr Bell said there were many different causes for nitrates and to single out dairy farmers was "extreme".
Gore bore Cooper’s Well, which has been plagued with nitrate issues since it was installed, is surrounded by just as many dairy farms as the issue-free Jacobs Town bore, he said.
ES general manager of science Karen Wilson somewhat agreed with Mr Appelbe, despite their investigation into July’s nitrate hike not identifying a "specific cause".
"It is likely to be the result of intensive land use in the area," she said.
The nitrate rise was declared by ES previously to be due to groundwater contamination.
Ms Wilson said many rural properties in Southland use groundwater and/or private bores for their water supply.
She encouraged these households to test their nitrate levels annually and preferably in spring or autumn, when nitrate levels tend to be higher.
In leaflets handed out at Thursday’s event, Greenpeace said bowel cancer risk increases by 4% for each milligram of nitrate.
It also said at 5mg/L pre-term birth increases by 47%, which Mr Appelbe said was confirmed by the New Zealand College of Midwives.
"This is all published research," Mr Appelbe said. "That’s what we’re led by."
The average sample from Gore homes on the town water supply tested by Greenpeace showed a nitrate level of about 4.8mg/L.
Mr Bell said a "less accurate" quick reading, which again had an error margin of 2mg, from council probes that day was 5.7mg/L.
The water-testing event will be at Waimate today, due to their "do not drink" notice last December, and Darfield on Sunday.
