Greenpeace campaigners say tests of bore water from across Southland show significantly elevated levels of nitrate contamination. 

The environmental lobby group, along with Forest & Bird, the Environmental Defence Society and Choose Clean Water, are calling on the Government to lower permitted level of nitrate in water to 0.87 milligrams per litre. 

They highlight international research linking nitrate contamination over that level to bowel cancer and over 5mg/L to adverse birth outcomes. 

Greenpeace tested more than 50 samples in Riversdale and over 30 in Winton at free drop-in sessions the weekend before last. 

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The samples came from as far afield as Lumsden, Riverton/Aparima and Kaka Point.

Initial analysis shows 86% of samples had over 0.87mg/L of nitrate contamination, while more than half were over the 5mg/L concentration.

Riversdale drinking water from multiple bores gave readings over 7mg/L and Winton town's water supply tested over 4mg/L of nitrate contamination.

Greenpeace campaigner Steve Abel says the results are very concerning.

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"Nobody should have to worry that their drinking water could make them sick," Abel says. 

"Unfortunately here in Southland, that is a very present worry for many communities, and a consequence of synthetic nitrogen fertiliser and dairy intensification."

Abel says that anecdotally, locals spoke about observing high rates of bowel cancer around Riversdale.

"The Government needs to act swiftly to ensure drinking water is safe, by lowering the limit on nitrate allowed in drinking water to under one mg/L and cutting nitrate contamination by phasing out synthetic nitrogen fertiliser and lowering stocking rates."

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The Government's current health limit is 11.3mg per litre of nitrate contamination.

But Environment Southland acknowledges that concentrations over 4mg/L show "significantly elevated" levels of nitrate contamination in drinking water, Abel says. 

Greenpeace tested 101 samples in Ashburton early this month. Analysis showed 61% of the samples had over 5mg/L of nitrate contamination. Ten samples were over the 11.3mg/L.

A 2018 Danish scientific study showed a significant increase in risk of bowel cancer at as low as 0.87mg/L of nitrate contamination in drinking water. A recent US study showed that at 5mg/L of nitrate contamination, the risk of premature birth increases by almost half.

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Southlanders were asked to bring 100mls of bore water in a glass or plastic container to the test days, held in Winton on Saturday, July 17, and Riversdale, Sunday, July 18.