Everyone should be able to trust that the water from their tap is safe to drink. Access to safe drinking water is a basic human right – but nitrate contamination of drinking water is putting people at risk. Scientists tell us that high concentrations of nitrate in water could be causing 100 cases of bowel cancer in New Zealand each year, and 40 deaths .
Research has shown a link to bowel cancer from long term exposure to nitrate in drinking water at much lower concentrations than the current legal limit of 11.3mg/L nitrate (NO3-N). An extensive Danish study found an increase in risks of bowel cancer from concentrations over 0.87mg per litre . There are also links to increased risk of preterm birth for pregnant people whose drinking water contains concentrations of 5 mg/L and higher .
Please read the information on this page for the answers to frequently asked questions.
If you need to talk to someone further about what your nitrate test result means, or if you would like to learn more about our work to ensure healthy drinking water for all and how you can be involved, please get in touch with us at [email protected]
What do the nitrate numbers mean?
Most New Zealanders (80%) drink water from their tap that has 1.0 mg/L or less of nitrate (NO3-N). However, around 800,000 New Zealanders could be exposed to levels of nitrate that are potentially harmful. The communities most likely to be exposed to elevated nitrate levels are those in rural areas on town groundwater and private bore water supplies.
The higher the nitrate concentrations in drinking water, the greater the potential health risks.
- 0.87 mg/l: A substantive study carried out in Denmark reported a link to bowel cancer at 0.87 mg/L of nitrate (NO3-N) and above  – showing potential health hazards from nitrate levels more than 11 times lower than our current health limit.
- 5.0 mg/l: On top of the bowel cancer risk, a recent US study found nitrate above 5 mg/L drunk by pregnant people increased the odds of a preterm birth by 47%, while exposure above 10 mg/L increased the odds of a preterm birth 2.5 times.
- 11.3 mg/l: Far above nitrate levels linked to these health risks is New Zealand’s current Drinking Water Standard for nitrate contamination. It was set decades ago to avoid only one condition – blue baby syndrome – and is “hopelessly out of date” according to public health physician Professor Michael Baker. It does not account for chronic illnesses like cancer.
There is sound evidence that having a source of drinking water with low concentrations of nitrate (under 1. mg/L) may avoid health risks.
Nitrate contamination in drinking water – what are the health risks?
For many years we have known that high concentrations of nitrate in drinking water used for mixing infant formula is linked to blue baby syndrome – where the nitrate deprives the baby of oxygen.
In New Zealand our drinking water standards have a maximum allowable value of nitrate-nitrogen (NO3-N) of 11.3mg/L, which was established by the World Health Organisation as the limit necessary to avoid blue baby syndrome. Public health physician Professor Michael Baker says the limit is “hopelessly out of date” because It does not account for chronic illnesses like cancer.
There is growing evidence that other health impacts occur with nitrate in water at much lower levels, including links between nitrate contaminated water and bowel cancers, thyroid disease, neural tube impacts, and premature birth.
An extensive Danish study  involving 2.7 million people over 23 years found a link to increased bowel cancer risk at only 0.87mg/L and above of nitrate in drinking water. A US study  found risks of preterm birth doubled at 5mg/L.
The New Zealand College of Public Health Medicine and Public Health Association has stated  that, “Excessive levels of nitrate pollution, from dairy farms, in drinking water is a direct threat to human health such as being linked to miscarriages in pregnant women. Long-term consumption of nitrate in drinking water is associated with the risk of several cancers such as thyroid, colorectal, non-Hodgkin’s lymphoma, stomach, bladder, breast, and ovarian.”
A 2021 scientific paper published internationally  found that in New Zealand nitrate in drinking water could be attributable to an additional 100 cases of bowel cancer per year and 40 deaths per year, and that around 800,000 New Zealanders (15%) have water supplies with potentially hazardous nitrate levels.
Many of the worst impacted communities are those on town groundwater or private bore water supplies in rural areas.
How does nitrate get into our drinking water?
While it is possible a leaking septic tank can cause high nitrate levels, if your tap water from a bore or groundwater supply shows elevated nitrate concentrations the odds are that it is caused by diffuse pollution from intensive agricultural activity in your area.
Synthetic nitrogen fertiliser and intensive dairying are the largest cause of increased nitrate contamination in our water.  The parts of New Zealand with high dairy cow numbers are also the regional hotspots for high nitrate concentrations in drinking water, including Canterbury, Waikato and Southland. We are also seeing high nitrate contamination in some market gardening areas such as Richmond in the Tasman District.
Two chemical companies – Ravensdown and Ballance – distribute 98% of New Zealand’s synthetic nitrogen fertiliser.
Synthetic nitrogen fertiliser is added to pasture to accelerate grass growth so excessive numbers of cows can be kept on the land. Most of the nitrogen that cows ingest passes through them and is excreted as urine and dung which leeches nitrate into groundwater. The indirect leaching of nitrate from dairy cow urine patches is the largest source of nitrate contamination. The dairy industry is the biggest spreader of synthetic nitrogen fertilizer using nearly 70% of New Zealand’s supply. In New Zealand we have seen a nearly sevenfold increase in synthetic nitrogen fertiliser use over the past 30 years , a doubling of the dairy herd, and worsening of nitrate concentrations in many groundwater wells. 
What can be done about nitrate in water?
Access to safe drinking water is a basic human right. Over 50% of New Zealanders rely on groundwater for their drinking water supply. The fertiliser and dairy industries are contaminating that vital supply and potentially turning people’s drinking water carcinogenic. Central and local governments must take responsibility for ensuring drinking water is safe by stopping nitrate contamination at its source.
New Zealand has one of the highest bowel cancers rates in the world. We also have high rates of bore water use, particularly in rural areas where nitrate concentrations are known to be worsening as a consequence of intensive dairying and the huge increase in the use of synthetic nitrogen fertiliser that enables excessive dairy cow numbers.
Greenpeace is calling on the Government and regional councils to ensure healthy water for all communities by lowering the limit on nitrate allowed in our water to under 1. mg/L; phasing out synthetic nitrogen fertiliser; lowering dairy cow stocking rates; and backing farmers to move to regenerative organic farming, so we can all live in a country where rivers run clear and our tap water is safe to drink.
What if my water test result shows elevated nitrate levels?
According to the United Nations,;“Access to safe water is a fundamental human need and, therefore, a basic human right. Contaminated water jeopardizes both the physical and social health of all people.”
Greenpeace believes polluters such as fertiliser companies Ravensdown and Ballance and the dairy industry should be held to account for the damage they do. It’s the job of regulators – such as local and central government – to prevent pollution, hold polluters responsible and protect people’s water from nitrate contamination.
There is sound evidence that having a source of drinking water with low concentrations of nitrate (under 1. mg/L) may avoid health risks. You can contact your regional council to advise them that you are not satisfied with the levels of nitrate in your drinking water.
They may recommend options such as reverse osmosis, drilling a deeper bore well or connecting to the town water supply. While nitrate can be removed from water using treatment processes such as ion exchange, distillation, and reverse osmosis, these can be expensive. Unfortunately boiling your water, mechanical filters, or chemical disinfection – such as chlorination – does not remove nitrate from water.
We recommend advising your regional council and local MP that you want them to take responsibility for the problem because local water users should not have to pay to fix contamination of their drinking water supply that is caused by fertiliser companies or intensive dairying in their area.
Support the call for the Government to lower the limit on nitrate allowed in drinking water to under 1. mg/L.
Don’t vegetables contain lots of nitrate?
Yes, vegetables are high in nitrate, but because they also contain antioxidants like vitamin C the process which leads to the creation of carcinogenic compounds from nitrates (called nitrosamines) is neutralised by the antioxidants. Eating plenty of fresh vegetables is good for general health and well being – and is in fact an important protection against illnesses like bowel cancer.
What do I do if I am concerned for my health?
It’s understandable to feel concerned about possible health impacts. If you are concerned for your health or the health of family members you can speak to a trained healthcare professional by calling Healthline on 0800 611 116.
If you are concerned for your mental wellbeing you can access further support via Lifeline on 0800 543 354 or can call or text 1737 to talk to a trained counsellor.
How can I get my drinking water tested for nitrate contamination?
Greenpeace is currently running a free mail-in nitrate contamination testing service for people who get their drinking water from a bore or a well.
You can order a sampling kit here.
References and links
- Richards J, Chambers T, et al, Nitrate contamination in drinking water and colorectal cancer: Exposure assessment and estimated health burden in New Zealand, November 2021: https://www.sciencedirect.com/science/article/abs/pii/S0013935121016236?dgcid=coauthor
- Schullehner et al. “Nitrate in drinking water and colorectal cancer risk: A nationwide population‐based cohort study.” International journal of cancer 143, no. 1 (2018): 73-79.
- Sherris Allison R, et al. Nitrate in Drinking Water during Pregnancy and Spontaneous Preterm Birth: A Retrospective Within-Mother Analysis in California. Environmental Health Perspectives. 2021;129(5):057001
- NZCPHM – New Zealand College of Public Health Medicine and PHA – Public Health Association. “Submission to the Ministry for the Environment: Action for Healthy Waterways” (2019)
- MFE and Stats NZ 2015 ”Environmental Reporting: Nitrogen leached from soil 1990–2012” – from the dataset accessed May 2021 at https://data.mfe.govt.nz/table/2530-nitrogen-leached-from-soil-total-1990-2012/data/
- Stats NZ. “Fertilisers – nitrogen and phosphorus” (2021) Accessed May 2021 https://www.stats.govt.nz/indicators/fertilisers-nitrogen-and-phosphorus
- Environment Canterbury 2016. “Annual groundwater quality survey,” Ten-year trends (2007 to 2016) in nitrate concentrations in annual survey wells, pg 7. Accessed May 2021: https://api.ecan.govt.nz/TrimPublicAPI/documents/download/3159733
- UN Secretary-General Statements and Messages, “ACCESS TO SAFE WATER FUNDAMENTAL HUMAN NEED, BASIC HUMAN RIGHT, SAYS SECRETARY-GENERAL IN MESSAGE ON WORLD WATER DAY,” 12/03/2001, https://www.un.org/press/en/2001/sgsm7738.doc.htm
Sign on now to call on the New Zealand Govt to ban chemical nitrogen fertiliser.