While publicly registered drinking water must meet government standards and regulations, people accessing private groundwater bores and springs supplying 25 or fewer people have no requirements to test their drinking water. Most of these groundwater self-supplies are found in rural areas and are vulnerable to nitrate contamination, leaving communities at risk if left untested.

A new study led by Earth Science New Zealand (formerly GNS Science) published in Science of The Total Environment analyzed data from more than 2,400 rural drinking water samples tested nationally between 2022 and 2024. The data was collected from several citizen-science community testing programs, including Earth Science New Zealand’s Nitrate Watch project, and programs run by Greenpeace Aotearoa, University of Canterbury, and Te Herenga Waka—Victoria University of Wellington.

The programs sourced samples through mail-in and town hall testing events, becoming an important vehicle to raise awareness of, and screen for, the presence of nitrate.

“This was a grassroots effort, and the first sampling campaign of this scale for Aotearoa New Zealand,” says Dr. Karyne Rogers, the lead author of the study.

“People from across the country have helped to build a national picture of nitrate contamination hot spots and received vital information about the nitrate levels of their own drinking water supply.”

The researchers found that 30.9% of the samples had more than half the maximum acceptable value (MAV) for nitrate that New Zealand’s Drinking Water Standards allow for publicly registered drinking water supplies, while 5.1% exceeded the MAV (142 samples).

“The results signal a widespread and concerning threat to freshwater quality across multiple regions,” Rogers says.

Canterbury, Waikato and Southland were the regions with the most samples that exceeded the MAV and also had a high number with more than half the MAV. Seven other regions were identified as regions with “emerging” nitrate issues, with 9.4% to 24.5% of rural groundwater self-supply samples above half the MAV.

Conny Tschritter, Earth Sciences New Zealand Groundwater Scientist and co-author of the study, says that these regions are not widely publicized as having challenges with nitrate in drinking water, and it is important that rural bore owners in the region can make informed decisions about monitoring their bores.

“Once we see a drinking water source approaching half the MAV, it’s a clear warning that there is nitrate contamination in the groundwater catchment, whether that’s due to increased land-use intensification or soils which are more vulnerable to excess nitrate leaching.”

Built with communities and for communities, this comprehensive dataset will help government authorities, iwi, farming and agricultural industries, and rural communities across New Zealand prioritize monitoring, guide mitigation, and support affected households.