The Gore water supply was deemed not safe for drinking on Friday afternoon last week because of nitrate levels in the water.
The ban on drinking from the supply was lifted on Monday night after three days of clear testing with the level well below the limit.
But University of Otago research fellow Dr Tim Chambers, who has studied nitrate concentration in water supplies, said it would not be the last supply round the country which will be impacted.
"We’ve been seeing it in the private suppliers for a while. Usually these public suppliers are better protected, but you know, the flood is coming, in terms of the nitrate contamination," he said.
"There’s only so much that the land can sustain and some of these suppliers, while they’re more protected than people in private suppliers, they’re not immune. They might be deeper bores or they might be better protected in some ways, but they’re generally still vulnerable."
He said nitrate contamination had been discovered when there had been changes in dairy intensification.
He said councils and other sectors had to be a little bit more deliberate about what land use was permitted in what areas, and to what intensity.
"It’s hard in some of these areas where you’re drawing from groundwater because the pollution can come from such an enormous area, because it all filters down into the same groundwater and then you’re pulling your water from there.
"Really, you have to have a catchment-level approach to the amount of nitrogen that you’re putting into the system. So it’s got to be done not at a farm level, because individual farmers might be doing different things that have different impacts on the overall quality, but it’s really what happens to the catchment that matters."
Gore had a nitrate reading level of 11.4mg per litre, 0.1mg above the 11.3mg maximum acceptable level.
Dr Chambers said the 11.3mg level was established in the 1950s and protected against one condition that affected only infants that are less than 6 months old.
"But there’s been quite a lot of research done in the last decade examining the relationship between nitrate and other health conditions."
He was leading a study in New Zealand looking at nitrate in drinking water and preterm birth risk, with the results due later this year.
"All of our environmental regulation related to drinking water is sort of establishing, well, ‘we can do this much land use until it hits that threshold’.
"But what we’ve been calling for for a long time is that you have to have a cautionary approach to this and trying to figure out that actually maybe it makes more sense to have a different threshold for where you start to intervene."
Greenpeace Aotearoa heaped the blame of the contamination on the intensive dairy industry — in particular, the overuse of synthetic nitrogen fertiliser.
Greenpeace spokesman Will Appelbe said the nitrate levels in Gore’s drinking water were only the beginning, as central government continued to relax standards on synthetic fertilisers.
"It is absolutely unacceptable that rural communities are unable to drink the water coming out of their kitchen tap — and this is happening more and more frequently," he said.
"Removing limits on fertiliser use will worsen the drinking water crisis and it’s only a matter of time before it proves to be dangerous."
But Federated Farmers Southland president Jason Herrick said Greenpeace was throwing out shots unfairly to promote its own agenda.
"I don’t think it’s a fair assessment. Greenpeace, they stick to one narrative and one ideological view and pick on something where it fits what they are trying to target."
Mr Herrick defended the use of synthetic nitrogen fertilisers. He said farmers adhered to the cap and it was too early to play the blame game.
— Additional reporting by Steve Hepburn
