December 26th, 2024
Ministry for the Environment and Manatū Hauora (the Ministry of Health) have co-authored a report, which was released on Friday, examining the potential risks associated with elevated nitrate levels in the country's drinking water, focusing particularly on South Canterbury bores.
Why it matters: Nitrate, typically originating from fertilisers and manure, can contaminate groundwater when it seeps into the soil. This issue has significant implications for public health and ecological wellbeing, and is particularly concerning for domestic self-suppliers who are potentially drinking from high nitrate sources.
The rising trend: An analysis of monitoring data revealed both increasing and decreasing nitrate concentrations at various sites. Alarmingly, 45.7% of monitored groundwater sites showed increasing nitrate levels over the past decade, creating 'nitrate hotspots' in areas like Canterbury, Southland, Hawke’s Bay, and Wairarapa. In the Canterbury region, some locales, including Seadown, northeast Ashburton, Tinwald, and the lower Hekeao/Hinds plains, are particularly affected.
In 2021, a survey of Canterbury Water Management Strategy 2009 (CWMS) bores found that 10% of the sampled sites had nitrate levels exceeding the maximum acceptable value (MAV) for drinking water. Between 2012 and 2021, 30% of the surveyed sites displayed 'very likely increasing' nitrate trends.
The implications: If nitrate levels continue to rise, water suppliers may need to halt operations, find alternative water sources or incur significant costs. Instances of nitrate levels exceeding the MAV have already occurred twice in 2022, rendering the reticulated water undrinkable for residents.
The MAV for nitrates in NZ's drinking water is set at 50mg/L NO3 (or 11.3mg/L NO3-N), intended to prevent Blue-Baby Syndrome, a condition caused by reduced oxygen availability. However, there's growing interest in potential health risks associated with nitrates in drinking water, including colorectal cancer and adverse reproductive outcomes.
The governmental response: With the enactment of the Water Services Act 2021, a more comprehensive regulatory regime is being established for monitoring and reporting nitrate levels in drinking water. This new regulation will extend to approximately 75,000 additional water suppliers previously unregistered under the Health Act 1956.
However, domestic self-suppliers are not subject to any monitoring or reporting regime, highlighting a crucial regulatory gap. Aiming to address this issue, the Ministry of Health will continue to monitor the evidence on nitrates in drinking water and update the recommended MAV should emerging evidence suggest a need to do so.
In light of this report, several recommendations have been put forth. The establishment of an inter-agency working group to monitor and respond to nitrate contamination in drinking water and a cooperative effort among the Ministry of Environment, Ministry of Health, and Taumata Arowai to standardise and share any monitoring and reporting of nitrates are among the crucial proposals.