Denmark to dramatically reduce limit for nitrate in drinking water - should NZ do the same?

What are the health risks associated with nitrate in drinking water?

The current NZ drinking water limit for nitrate is 11.3 mg/L (as nitrate-nitrogen, equivalent to 50 mg/L as nitrate). The World Health Organization (WHO) established this limit in 1958, and retained it after reviews conducted in 2003 and 2016.¹ More recently, studies have found elevated colorectal cancer risk at nitrate concentrations below this limit,² including a national study in Denmark.³ In response, at least four countries have initiated reviews of health risks associated with nitrate,^4-7 including the most thorough completed assessment in Denmark.⁷

What were the results of the Danish process? 

The Danish Ministry of Environment and Gender Equality has requested a series of reports since 2019 on whether the current nitrate limit sufficiently protects public health. A 2024 report concluded that, although uncertainties persist, the epidemiological evidence for colorectal cancer indicates that nitrate in drinking water poses a health risk. In 2025, an international expert group was tasked with deriving a new limit and recommended 1.3 mg/L. Following the 2026 General Election, the coalition agreement included a commitment to implement this advice with immediate effect alongside further restrictions on nitrate-sensitive drinking water areas.

Why does this matter in NZ?

Nitrate levels in freshwater are increasing in many areas of NZ. For example, Environment Canterbury’s 2025 Annual Groundwater Quality Survey found 10% of wells exceeded the current limit for drinking water (11.3mg/L), with 62% of long-term sites showing increasing nitrate trends, leading to the council declaring a nitrate emergency in 2025.⁸ Recent exceedances in public supplies in Waimate and Gore have forced short-term “do not drink” responses and long-term acceptance of elevated nitrate levels.^9,10 People relying on their own drinking water supplies, defined as domestic self-supplies, are particularly vulnerable as they often rely on shallow groundwater sources that are susceptible to nitrate contamination.¹¹ Figure 1 shows the measured nitrate levels in public registered supplies (data up to 2024), that exceed the Danish limit of 1.3 mg/L.

Figure 1: Measured nitrate levels in public registered supplies (data up to 2024).

What can be done about it?

Taumata Arowai and Ministry of Health: Review of the current limit

NZ currently aligns most of its drinking water standards with WHO guideline values. However, the WHO reviews specific water-quality parameters only intermittently. For example, nitrate was last reviewed in 2016,¹² following an earlier review in 2003.¹³ It seems unlikely nitrate will be prioritised in an upcoming review. Government actions could therefore include: 1) petition the WHO to prioritise the review the nitrate guideline value; 2) commissioning a bespoke assessment of the nitrate limit in the NZ context. The Ministry of Health is currently undertaking a technical review of nitrate risks for human health, due to be completed at the end of this year.¹⁴ However, it is unclear what this involves.

Taumata Arowai: Clarify roles, responsibilities and systems of accountability

Additionally, Taumata Arowai needs to formally clarify responsibilities regarding drinking water source protection between itself and regional councils. A lack of explicit delineation of roles is leading to different interpretations of existing laws and gaps in responsibility and accountability.⁹ It is also delaying the actions needed to reduce pollution of drinking water and forcing additional costs and complexity of treating drinking water onto drinking water suppliers, such as district and city councils.⁹

Central government: Rewrite Resource Management Act reforms to give strong protection for drinking water sources

There is a high risk that the Government’s proposed replacements to the Resource Management Act will establish little to no protection from nitrate contamination for drinking water sources. This is outlined in full in this previous Briefing.¹⁵ However, reforms are still under consideration through a select committee process.

Regional Councils: Evaluate existing plans efficacy for protecting drinking water sources, review data collection and identify gaps, commission independent review of conflict-of-interest management with regards to decisions on drinking water.

In many areas, regional plans have failed to protect drinking water sources from nitrate contamination.^9,10,15 We previously covered three key areas in this previous Briefing that regional councils could prioritise regardless of the changing regulatory environment.¹⁶ These included: commissioning an independent evaluation of drinking water source protections; a complementary review of data availability, suitability and collection; and a review of conflict-of-interest processes.
 

Authors' details

Associate Professor Tim Chambers, Ngāi Tahu Research Centre, Te Whare Wānanga o Waitaha | University of Canterbury

Marnie Prickett, Research Fellow, Department of Public Health, Ōtākou Whakaihu Waka, Pōneke | University of Otago, Wellington

Professor Simon Hales, Department of Public Health, Ōtākou Whakaihu Waka, Pōneke | University of Otago, Wellington