ECan’s ‘Nitrate Emergency’: Good step but here is a more robust path for region’s drinking water

How bad is the problem?

Across Canterbury, nitrate and microbial contamination have increased with land-use intensification. ECan’s 2025 Annual Groundwater Quality Survey found 10% of wells exceeded the nitrate maximum acceptable value (MAV) for drinking water (11.3 mg/L as NO₃-N), with 62% of long-term sites showing increasing nitrate trends.¹ Recent exceedances in the Lower Waihao rural scheme in Waimate have forced short-term “do not drink” responses and long-term acceptance of elevated nitrate levels.² Likewise, a recent survey of domestic self-supplied bores in the Selwyn District also found widespread nitrate contamination beyond the drinking water MAV, consistent with wider environmental monitoring (Figure 1).

The predominant source of nitrate in Canterbury is dairy cattle (Figure 2), which have increased in population from 113,000 in 1990 to 1.25 million in 2022 (nearly a 10-fold increase; see Figure 3). Other sources of nitrate contamination can include septic tanks and other land use, which can cause localised contamination of water. At a regional level, however, dairy cattle are the main source.

Figure 1: Nitrate-nitrogen leached from livestock in 2017 as reported by Statistics New Zealand

Figure 2: Agricultural land use in Canterbury/Waitaha in 2019 by dairy density (blue) and sheep, beef & deer density (purple) as reported by Environment Canterbury (ECan)

Figure 3: Percent change in land use factors from baseline to current state in the Canterbury Region 

What is ECan responsible for?

Source water protection is a core part of drinking water safety and is central to reducing risk from both chemicals, like nitrate and pesticides, and human pathogens such as Cryptosporidium, E. coli, and Campylobacter.³ In its review of national drinking water supply systems, the Government’s Havelock North Drinking Water Inquiry affirmed that source water protection “provides the first, and most significant, barrier against drinking water contamination and illness.”³ As the regional authority, ECan is responsible for managing land and water use under regional plans, setting limits for pollution, issuing and enforcing resource consents for activities impacting water quality, and designating drinking water protection zones. As such, ECan is the key regulatory agency responsible for the protection of source water used for drinking water in Canterbury.

Treatment of water is unlikely to be a viable long-term solution. Nitrate removal from drinking water is technically feasible but expensive and complex to build and run, with waste brine disposal and ongoing costs (see Appendix 3). 

What are the emerging potential health concerns?

The current MAV for nitrate protects against “blue baby syndrome” (methaemoglobinaemia), which can be fatal in bottle-fed infants less than 6 months old.⁴ However, emerging epidemiological evidence indicates other health risks may occur below this contamination threshold. A set of studies has found elevated colorectal cancer (CRC) risk at relatively low nitrate in drinking water,⁵ including a national study in Denmark over many decades.⁶ For pregnancy outcomes, epidemiological studies have observed associations between drinking-water nitrate and preterm birth and certain congenital anomalies,⁷ although uncertainty on causality and the magnitude of the effect remain. Overall, the weight of the emerging scientific evidence supports precautionary reductions in nitrate exposure, especially for pregnant people and infants. Today, several authorities are actively re-examining health risks associated with nitrate (outlined in Table A2). 

Is the Central Government helping or hindering ECan’s work on nitrates? 

Agricultural Minister Todd McClay said of Ecan’s declaration that it did a "disservice to an important issue the Government is focused on getting right". However, the Government has removed or is proposing to remove, weaken or delay many of the policy and regulatory tools regional councils have to address drinking water source pollution.

Despite the Government removing hard-won protections for drinking water sources, ECan and its elected councillors are not without power. The motion includes useful actions but, in our view, are insufficient to make decisive progress. 

In March this year, we provided a briefing to ECan councillors on the extent of nitrate contamination to drinking water sources and potential ecological and health impacts (see full presentation here). 

Our briefing concluded with recommendations for ECan that could be acted upon, regardless of any central government policy changes, which are reproduced here (with minor adjustments):

• Commission an independent evaluation of drinking water source protections, with the research question: Can existing plans and rules achieve existing limits for drinking water sources? This evaluation must be independent (ie, external) and peer-reviewed to ensure its rigour and overcome any bias.
• A complementary review of data availability, suitability and collection: Does ECan have access to the necessary data to make informed decisions to protect and improve drinking water sources?
• Request Auditor-General review of conflict-of-interest processes for councillors and council staff: There is a high risk that conflicts-of-interest could undermine responsible decision-making on drinking water quality and Cantabrians need confidence that conflicts are not compromising decisions on their drinking water which might impact their health and possible risk of cancer.