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After Greenpeace Aotearoa tested bore water in Riversdale last week, senior campaigner Steve Abel said he was "very concerned" about how high nitrate-nitrogen levels were in the town’s water samples.

"In fact 100% of them were over the 5mg/l which is the risk for pre-term birth and all of them are well over the cancer risk limit of 0.87mg/l," Mr Abel said.

A Danish study had shown there was a link between bowel cancer and nitrate-nitrogen levels of 0.87mg/l, he said.

Levels of nitrate-nitrogen in water samples taken from 28 bores in the town ranged from 5.19mg/l to 8.88mg/l.

The maximum level allowed in New Zealand is 11.3 mg/litre, which is the level set by the World Health Organisation (WHO) as the limit necessary to avoid blue baby syndrome.

The Otago Daily Times approached the Ministry of Health for its perspective on Mr Abel’s claims.

A ministry spokesman said if Riversdale residents were concerned about the level of nitrate in their private bores they should continue to test the water regularly.

"We would suggest that they switch to an alternative supply with the highest quality source water possible or install a point-of-use ion exchange device."

Once the Water Services Bill is passed, Taumata Arowai will take over from the Ministry of Health as water services regulator for the country.

At present, the Bill is at the select committee stage of the legislative process.

Taumata Arowai would require all water supplies to monitor for nitrate and other chemicals in their first year of operation, the ministry spokesman said.

In 2019, the ministry contacted the WHO to find out whether it planned to review the nitrate guideline values in light of the Danish study linking nitrates to bowel cancer.

The WHO responded that while it was possible ingesting nitrate could cause cancer in humans, other studies had shown conflicting data.

It concluded the Danish study did not establish nitrate in drinking water caused colorectal cancer.

sandy.eggleston@odt.co.nz