Media release: Should NZ follow Denmark and dramatically cut nitrate limit for drinking water?

The Danish Government has decided to follow the advice of an international panel of experts and dramatically reduce the nitrate limit for drinking water to give greater protection for human health. 

Experts here are asking if Aotearoa New Zealand (NZ) should do the same.

In the latest Public Health Communication Centre Briefing, Associate Professor Tim Chambers from the University of Canterbury and co-authors, highlight the importance and implications of this development for NZ.

“Nitrate contamination of the groundwater, which many New Zealanders rely on for drinking water, is widespread and increasing in many regions,” says Assoc Prof Chambers.

“Given the growing body of epidemiological evidence and the slow pace of international guideline reviews, our government should consider a dedicated reassessment of the current limit, such as the one undertaken in Denmark.”

Denmark’s new limit is based on an independent international expert assessment, commissioned by its Ministry of Environment, which concluded that existing evidence indicates an increased risk of colorectal cancer at concentrations well below current guideline values. Based on this assessment, Denmark’s nitrate limit for drinking water will go from 11.3mg/L to 1.3mg/L to give greater protection for human health. 

NZ currently uses the 11.3mg/L limit, which was established by the World Health Organization (WHO). This limit was established in 1958 to protect against infant methemoglobinemia (Blue baby syndrome) and was retained after reviews conducted in 2003 and 2016. 

However, more recently, studies have found elevated colorectal cancer risk at nitrate concentrations below this limit, including a national study in Denmark. In response, at least four countries have initiated reviews of health risks associated with nitrate, including the most thorough completed assessment in Denmark. 

“These findings are relevant to NZ because, like Denmark, we have significant issues with nitrate contamination of drinking water sources, primarily from agricultural pollution. Our public agencies with responsibilities for drinking water and public health should consider undertaking a process like Denmark’s as well as advocate to the WHO to prioritise a review of the health impacts of nitrate in drinking water,” says Chambers.

It has recently been reported that the Ministry of Health is conducting a technical review, however it is unclear what this entails. Chambers says he would like the Ministry to release its terms of reference for the review so that its methodology can be assessed.

The Briefing also notes that in previous work, the authors have documented the gaps in responsibility and accountability for the protection of drinking water sources. The authors say Taumata Arowai (the national drinking water regulator), central and local government need to clarify their roles to fill these gaps to slow and begin to reverse nitrate contamination of communities’ drinking water sources. 

They also reiterate that the resource management reforms under consideration by the Government offer little protection for drinking water sources and should be rewritten.

“Good quality drinking water is critical to our health and well-being, and our public agencies have a responsibility to ensure that it can be provided to all our communities for generations to come.”