Canterbury water testing raises health concerns

  • 27/11/2018

Canterbury water testing raises health concerns

Fish & Game has carried out sampling in Canterbury -  knowing that nitrates contamination in rivers kills trout - to see whether contamination from intensive dairy farming is getting into drinking water.

The recent testing shows nitrate contamination has increased to levels that have been shown to be associated with an increased risk of cancer in humans.

Fish & Game worked with Dr Mike Joy who carried out the nitrate nitrogen testing of 114 drinking water samples from across the Canterbury plains, to find that more than half of them were above the 3.87 level.

Top right: Dr Mike Joy used a Nico real time nitrate-nitrogen tester to test water samples.

This finding is a major concern as it is the level where colorectal cancer risk increases significantly.

One of the world’s largest ever studies on the impacts of nitrates in drinking water in Denmark confirmed that nitrate levels above 3.87 mg/1000ml substantially increases the risk of colorectal cancer (CRC).

In Canterbury, even more concerning, 46 samples tested were above 6 mg/1000ml of nitrate-nitrogen which in New Zealand is seen as the trigger point for concern by health authorities.

This situation will get worse in future as nitrate levels are increasing and predicted to do so for decades, says Fish & Game Chief Executive Martin Taylor.

“The main source of nitrates contamination in Canterbury water comes from intensive dairy farms who use large amounts of fertiliser and from dairy cow urine.

“Samples were provided in a citizen science project by concerned Cantabrians wanting to know more about their own drinking water, and from sampling of public water supplies at sports grounds and public facilities.”

Mr Taylor says that “some detractors will say this is scare mongering – It is not. 

“All we have done is test water and compare those results to the latest research which has confirmed what is happening and is going to continue happening in the future”.

The true impact of intensive dairy farming in Canterbury is not only about destroying habitat for trout, eels and whitebait, it is now impacting on many peoples’ health, he says.

Mr Taylor says the first thing that needs to happen is to stop allowing more cows on the Canterbury Plains. 

“Second, the use of nitrate laden fertiliser must be regulated and reduced as soon as possible.

“Thirdly, Fonterra, Dairy NZ and Federated Farmers need to work out how they are going to pay for clean safe drinking water for those families and communities affected by their members’ business,” he says.

“Every litre of milk produced in New Zealand is increasing the nitrate levels in ground water and the costs of cleaning up nitrate contamination should fall on the businesses who make a profit from putting it into the water in the first place”.

Frequently asked questions:

What is Nitrate:

Nitrate (NO3) is a compound that is formed when nitrogen combines with oxygen. The main adult intake of nitrate is from food rather than water; but sometimes high amounts of nitrate get into drinking water.

What is the safe nitrate contamination level for drinking water in NZ?

Drinking Water Standards for New Zealand set a Maximum Acceptable Level (MAV) of 50mg/L for nitrate, which is equivalent to 11.3mg/l nitrate-nitrogen. Some laboratories report nitrate levels whereas other report nitrate-nitrogen, ensure that you are aware which they are reporting if you are getting your water tested.

How does nitrate contamination get into drinking water?

Typical sources of nitrate include; fertilisers, animal wastes, particularly in areas of intensified farming, unreticulated sewage disposal systems, industrial waste and food processing waste. Nitrate is highly soluble in water, making it readily transported through the soil to groundwater.

Are the nitrate contamination levels in Canterbury’s aquifers going to increase or decrease in the next 20 years?

Indications from studies done by Environment Canterbury are that nitrate levels will increase, their latest report is available here:

Can you take out nitrates from drinking water?

Nitrate is difficult to remove from water. Common household cartridge or carbon filters, boiling water and chemical treatments (e.g. chlorine) will not remove nitrate. There are three methods that do remove nitrate from drinking water: distillation, reverse osmosis and anion exchange. These processes are expensive and potentially unreliable.

Where in Canterbury are the risk areas?

You can download regional maps from this site which will show your risk level:

Where can I go to get my water tested?

It is important to use a laboratory which has been approved by the Ministry of Health to carry out the analysis required.

Below are some laboratories that can test drinking water for nitrate and E coli.

For nitrate, results should not exceed 50mg/L nitrate (which is equivalent to 11.3mg/L nitrate-nitrogen). Please check how the results are expressed.

* Eurofins 03 3435227

*Hills Chemistry 03 3777176

* Citilabs 03 4557938

Prices for nitrate analysis range from $11 plus GST to $30

I’ve had my water tested, where can I go for more advice?

Community and Public Health has more information on their website or call them on  03 364 1777.

Academic Articles on Nitrate and/or Canterbury

  1. Nitrate in Drinking Water and Colorectal Cancer Risk.  International Journal of Cancer 2018.

Individual nitrate exposure was calculated for 2.7 million adults based on drinking water quality analyses at public waterworks and private wells between 1978 and 2011. For the main analyses, 1.7 million individuals with highest exposure assessment quality were included……We found statistically significant increased risks at drinking water levels above 3.87 mg/L, well below the current drinking water standard of 50 mg/L.


2. Nitrate discharge to ground water from agricultural land use: an initial assessment for the Canterbury Plains.  2009

Nitrate discharge from agricultural land use on the Canterbury Plains has the potential to cause levels of nitrate concentration in shallow groundwater (<20metres below the groundwater surface), at some localities, that exceed the drinking water standard.  Groundwater quality generally improves with depth below the groundwater surface because of dispersive mixing with high quality groundwater from river recharge.

3. ECAN Reports on Nitrates in Drinking Water

The samples from 22 wells (7.0%) had nitrate nitrogen concentrations above the health-based Maximum Acceptable Value (MAV). This was very similar to the previous year’s survey (22 wells and 6.7% of sampled wells). E. coli were detected in the samples from 25 wells, which was an increase from the previous survey (22 wells).

4. ECAN Website on Drinking Water Quality

Canterbury has some of the best drinking water in the world, but no water supply is completely without risk. If you get your drinking water from your own private well, there are some things you should know.


More Posts