The research, by the universities of Otago, Canterbury and Massey, found a small but consistent increase in the risk of preterm births as nitrate concentrations increased — even at levels well below the present drinking water standards.
A ministry spokeswoman said the it initiated a technical review of the human health effects of drinking water earlier this year, to support The Water Services Authority — Taumata Arowai’s upcoming review of the Drinking Water Standards.
‘‘The ministry’s review will consider publications from January 2021 to February 2026, focusing on the human health effects from nitrates in drinking water.
‘‘The ministry keeps a watching brief on the evidence around nitrates in drinking water, including any new publications on the subject, such as this one.
‘‘Relevant substantive studies, including local New Zealand research, may also be considered in the review on a case-by-case basis.’’
The lead author of the new study, University of Canterbury environment health researcher Associate Prof Tim Chambers, said the research analysed 735,831 single baby births between 2008 and 2021, linking gestational age with estimated nitrate concentrations in drinking water at the mother’s usual residence.
About one in 15 babies in New Zealand are born preterm — before 37 weeks — which increases the risk of health problems.
The present maximum acceptable value (MAV) for nitrate-nitrogen in drinking water is 11.3mg per litre — a standard established nationally by Taumata Arowai, based on health advice from Health New Zealand Te Whatu Ora.
Denmark recently decided to lower its drinking water standard for nitrates to 1.3mg per litre, based on an international expert assessment of increased risk of colorectal cancer.
Other studies have shown that in New Zealand, up to 100 cases of bowel cancer and 40 deaths a year could be caused by drinking water nitrate contamination.
Most public drinking water supplies in New Zealand have low nitrate concentrations, the majority below 1mg per litre.
However, two municipal supplies, Gore and Waimate, were highlighted in Assoc Prof Chambers’ research because they recently breached the existing New Zealand standard for nitrates in drinking water.
The spokeswoman said the MAV for nitrates in New Zealand’s drinking water was ‘‘consistent with international guidelines, including the World Health Organization, the European Union and Australia’’.
‘‘In New Zealand, the level of nitrate in urban water reticulated supplies tends to be very low
...
‘‘We are aware there are some rural water supplies where the nitrate level has at times been higher than the maximum acceptable value.
‘‘If a member of the public believes their drinking water is not safe, they can raise their concern directly with their drinking water supplier.’’
Gore District Council critical services manager Jason Domigan said staff took their responsibility of providing safe drinking water very seriously.
‘‘We will continue to monitor developments in the science and follow any direction provided by the relevant regulators.
‘‘[The] council takes all credible scientific research relating to drinking water and public health seriously, and welcomes ongoing research in this area.
‘‘If Taumata Arowai reviews the emerging scientific evidence and decides to amend the national standard in the future, Gore District Council would respond accordingly.’’
Environment Southland general manager Karen Wilson said the main reticulated drinking water suppliers in Southland were Invercargill City Council, Southland District Council and Gore District Council, and they were all responsible for the water they provided to users.
Environment Southland was responsible for managing land use activities that could compromise the safety of drinking water sources by placing conditions on resource consents so that drinking water suppliers were immediately notified if spills or significant events occurred and contributing to source water risk management plans by monitoring quality and sharing hazard information, she said.
Environment Southland released a report earlier this year based on decades of data, monitoring and investigations.
The report helps clarify the complexity of nitrate levels in Southland’s groundwater.
It was commissioned as part of the initial response to the nitrate spike in Gore’s drinking water to bring together decades of published research, monitoring data and regional modelling, and to present it in an accessible way, making it easier for communities and decision-makers to understand and respond.
‘‘As part of this ongoing response, Environment Southland is continuing scientific investigations and monitoring; working alongside agencies responsible for drinking water protection; supporting improved land management practices and farm planning; and engaging with landowners and communities on local solutions to improve water quality.
‘‘Environment Southland considers this an important issue for Southland and is increasing its ongoing action to protect water quality at its source.’’
