Concern as nitrate levels rise in half of wells tested in Canterbury

Monday, 26 July 2021

Water samples from Temuka residents at a recent water nitrate testing event run (file photo).

Groundwater nitrate levels are on the rise in nearly half the wells Canterbury’s regional council regularly tests, with some soaring well past international health guidelines.

Environment Canterbury (ECan) has released the results of its annual groundwater quality survey for 2020, which tests for levels of contaminants like nitrate-nitrogen and E.coli bacteria in bores and wells across the region.

Researchers tested 322 wells, and found an average nitrate level of 2.7 milligrams per litre. The highest level detected was 22mg/L, nearly double the World Health Organisation’s (WHO) recommended 11.3mg/L drinking water limit.

Twenty wells total were above the 11.3mg/L limit, with 13 of those in the heavily-farmed Ashburton area.

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Ashburton also had the lion’s share of wells exceeding New Zealand's drinking water standard for E coli – one bacterium per 100 millilitres of water – with 15 of the region’s 37 over the limit.

The report also showed nitrate trends over recent years.

Selwyn residents with private wells had the opportunity to test their nitrate levels in Darfield. Video first published in May 2021.

For the wells with enough data, 47 per cent had nitrate concentrations logged as likely increasing over the past decade.

Twenty-eight per cent showed little change, and 25 per cent of wells had nitrate levels believed to be decreasing.

ECan groundwater science manager Carl Hanson said the results were not unexpected, with 11 per cent of wells tested over the E coli limit, and six per cent over the nitrate-nitrogen limit.

All the limit-busting wells were privately-owned, he said.

ECan says nitrate concentrations in Canterbury’s groundwater have been increasing for years, due largely to nutrient losses from farmland (file photo).

“The owners of all of these wells have been notified. Most of them are not used for drinking water.

“Some owners have installed filters if they are drinking the water, others have replaced the wells – but we still monitor old wells for our long-term trend analyses.”

Hanson said nitrate concentrations in Canterbury’s groundwater had been increasing for many years, due largely to nutrient losses from agricultural land.

Farmers used synthetic nitrogen fertilisers to add nutrients to the soil, some of which were then ingested by cows and excreted.

“Environment Canterbury takes nitrates very seriously. Canterbury has some of the strictest land-use rules in New Zealand to protect the region’s water quality,” Hanson said.

“Over time, these steps will help ensure that less nitrate enters Canterbury’s water.”

While ECan was responsible for groundwater health in the region, Hanson said people with private drinking wells were responsible for making sure their supply was safe.

Greenpeace spokesman Steve Abel at a recent Greenpeace water nitrate level testing day.

“Make sure your well is secure and test your water periodically. In most cases, samples can be taken from a kitchen tap and sent to a lab for testing at your own expense.”

But some were concerned the WHO drinking water nitrate level was much too high.

The 11.3mg/L limit is more than 10 times higher than 0.87 mg/L, the level linked to increased bowel cancer risk in a major Danish study published in 2018.

New research released this year found the chances of a premature birth increased by 47 per cent when nitrates in drinking water were just 5 mg/L.

Greenpeace campaigner Steve Abel said the 11.3mg/L limit was for one health condition only – blue baby syndrome – and given the mounting evidence there was no guarantee even water under that level was safe.

The group recently held free water nitrate testing sessions across Canterbury, where around 450 private bore samples were tested.

Abel said ECan’s data confirmed what they found, particularly “concerningly high levels of nitrate contamination” around Ashburton.

“Locals in these areas are rightly concerned for their health and feel frustrated at the lack of options for those with high levels of nitrate contamination in their drinking water.

“No one should have to wonder if their tap water could be making them or their family sick. Everyone has a right to safe drinking water.”

Abel was not convinced “farm plans” would solve the problem.

“We need central and regional government to put people’s health first and stop the contamination of drinking water at source, by cutting synthetic nitrogen fertiliser and lowering dairy cow stocking rates.”