Drinking Water At Risk
Introduction
Access to safe and reliable drinking water is a basic human right, yet around one-third of New Zealanders rely on supplies that are inadequately protected.
Within the Ngāi Tahu Takiwā, eleven marae depend on unreticulated water systems, meaning they are not connected to council networks and must manage their own supply. These marae, and many rural communities, face a greater risk of drinking water contamination.
Intensive dairy farming has contributed to elevated nitrate concentrations in groundwater, particularly in Canterbury and Southland.
This contamination not only degrades freshwater ecosystems but also poses public health risks, including links to colorectal cancer. Microbial contamination, such as E. coli, adds further concern, with some kāinga already experiencing unsafe or declining drinking water quality.
Regular testing, better monitoring, and targeted investment are essential to protect the safety and reliability of rural and marae water supplies. This prompted Te Kura Taka Pini to undertake its own monitoring and surveillance, through the Māngai Wai Māori programme.
Nitrates in Our Water
One of the key issues for TKTP is the rising level of nitrates in our drinking water. Nitrate is a nutrient that helps plants grow, and while it occurs naturally, the widespread use of synthetic fertilisers has significantly increased nitrate concentrations in the environment. When nitrate is applied to land, it can leach into surface water and groundwater, eventually entering drinking water supplies.
Current Standards and Concerns
New Zealand’s drinking water standard for nitrate-nitrogen is 11.3 mg/L, a limit originally based on the World Health Organization’s (WHO) guideline value, which was set to prevent infant methemoglobinemia (blue baby syndrome). However, this standard does not reflect the broader health concerns highlighted in newer studies, and many experts now believe it may be too high to ensure public safety.
It is also important to note that New Zealand’s drinking water standard allows much higher nitrate concentrations than environmental standards. Under the National Policy Statement for Freshwater Management, the bottom line for nitrate-nitrogen is much lower, at 2.4 mg/L, and is set to protect aquatic life. Above this level, nitrate is toxic to fish and freshwater invertebrates.
Nitrate Contamination: What Recent Research Is Showing
Long-term exposure to nitrates in drinking water may pose health risks, even at levels well below New Zealand’s current limit. New research has identified links between nitrate consumption and elevated risks of colorectal cancer, pre-term birth, and low birth weight — raising important questions about whether existing guidelines are protective enough.
Nitrate Contamination: What the Data Tells Us
Nitrate levels in groundwater are rising across the country. Recent studies show:
- A survey of more than 2,400 rural drinking water supplies found that Canterbury had the highest proportion of nitrate-contaminated bores, while Southland recorded the highest single nitrate reading at 140 mg/L — more than 12 times the legal limit.
- Across New Zealand, 12.4% of monitored groundwater wells exceed the Maximum Acceptable Value for nitrate-nitrogen (11.3 mg/L), with some recording levels as high as 28 mg/L.
Rising nitrate contamination and mounting health concerns led Environment Canterbury to declare a nitrate emergency on 17 September 2025, signalling the need for urgent action to protect drinking water sources and community wellbeing.