Nitrate in waterways

Why is nitrate an issue?

Nitrate is a chemical compound made of nitrogen and oxygen. It occurs naturally in soil, where it is a major source of nitrogen for plants, helping them grow.

Nitrate – or too much of it – can be a problem because:

• When soil contains more nitrate than plants can use, the excess can be washed through by rainwater and carried into the underlying groundwater.
• If groundwater feeds springs that flow into streams or lakes, the nitrate can cause excess weed growth, algal blooms and toxicity for fish and invertebrates.
• If groundwater is used as a source of drinking water, nitrate can pose a health risk.
• Nitrate concentrations can spike after heavy rainfall, especially if that rainfall follows a long dry period.

Nitrate concentrations in drinking water

High nitrate concentrations in drinking water may cause health issues for people as well as to the biological health of waterways.

Taumata Arowai, the water services regulator established in 2021, sets the threshold to protect against the particular threat to bottle-fed babies.

Various studies have looked into possible links between nitrate concentrations and colorectal cancer.

The Prime Minister's Chief Science Advisor has produced a report, and we support calls for more research on any possible links between nitrate concentrations and human health.

However, as a regulator, we follow the lead from national health authorities on determining safe limits of contaminants in drinking water.

What we’re doing to address the issue

Regional councils have certain roles and powers under legislation – as well as the ability to work with mana whenua, industry and stakeholders – to act within our mandate to mitigate nitrate losses to the environment.

This means there are actions that Environment Canterbury, as the regional council, is doing to address this issue. But it is not something we can solve on our own, and many other entities are also involved.

The actions we are undertaking include:

• Supporting farmers: Canterbury farmers are making progress in reducing nutrient and other contaminant losses within their farming systems. Our land management advisors are supporting them with this work, raising awareness and encouraging best practices, including: 
  • • nitrogen use efficiency
    • winter grazing  
    • critical source area management.
• Protecting and promoting wetlands: We’re focused on identifying and protecting Canterbury’s remaining wetlands by providing better information and incentives for landowners to protect existing wetlands, as well as making it easier for landowners to create constructed wetland areas that can act as filters to remove nitrate and other contaminants from freshwater.
• Keeping it local: We’re working with and funding communities at a catchment level to empower them to take the initiative and innovate for water quality solutions.
• Reviewing our planning framework: We’re undertaking a review of our current plans to get a clearer picture of the state of our environment and to measure the effectiveness of our current policies. However, we cannot currently propose new changes to our planning framework due to central government’s changes to the resource management system.
• Improving resource consents: We’re strengthening new resource consent conditions and clarifying our expectations on how consent holders can demonstrate compliance with these conditions. We’re sharing examples of these typical conditions that consent applicants can propose, which can be tailored so they are appropriate for the local environment where the proposed activity will take place.
• Improving compliance work: We’re prioritising compliance monitoring for the highest-risk activities, as well as activities in community drinking water protection zones and other areas with especially sensitive environments or already degraded water quality.
• Taking compliance action: We’re ensuring we take appropriate compliance action when the right thing isn't done – from education and on-farm support through to enforcement when needed.

How landowners are making a difference

While we can set rules and measures, the real work in reducing nitrogen loss comes from those who work the land. Our farming community has made huge strides to invest in new technologies and adopt new tactics to stop nutrient leaching. These tactics include fencing, riparian planting, stock management, irrigation efficiency, strategic grazing, planting catch crops, better use of fertiliser and more. They're demonstrating this in Farm Environment Plans, and our audit results are showing that more and more Canterbury farmers are applying these tactics to reduce their impact on freshwater.

Progress and challenges in protecting Canterbury’s water

Over the past 10 years, the Canterbury Water Management Strategy, Canterbury Land and Water Regional Plan, and its later, sub-regional updates have started to address the problems caused by land-use intensification.

Some of the impacts of these new rules are only starting to take effect, and while much good work has already been done by landowners, Rūnanga, community groups and others, there is much still to be done.

This contributes to our environmental protection and regulation core service, where we work with mana whenua, stakeholders and communities to promote sustainable management of natural resources and protect and enhance the health of the natural environment.

Nitrate concentrations will continue to cause problems in spring-fed streams and lakes for some years. While the drinking water from Christchurch’s deep aquifers remains relatively clear of contaminants, and other council supplies are kept safe to drink, anyone using a private well for drinking water needs to be aware of the risk.

Nitrate monitoring and reporting

Groundwater reporting

We monitor groundwater quality in over 300 wells across the region each year, with nitrate concentration just one of the water quality measures.

Nitrate lag report

In 2023 we published How long will it take? A summary of information about nitrate time lags in Canterbury (PDF, 3.53MB), which found that major land use changes should result in improvements in groundwater quality within five to 10 years.

Groundwater Quality Report

Each year we take samples from more than 300 wells across Canterbury as part of our annual groundwater quality survey. Among other findings, over the last few years we've consistently found that nitrate-nitrogen concentrations are likely increasing in more than half of samples, while around a quarter show no trend, and less than a quarter show a likely decrease in nitrate-nitrogen concentrations.

Download the findings from our surveys:

 Annual Groundwater Quality Survey 2024 (PDF file, 3.38MB)

Annual Groundwater Quality Survey 2023 (PDF, 10.0MB) 

 Annual Groundwater Quality Survey 2022 (PDF, 9.68MB)

 Annual Groundwater Quality Survey 2021 (PDF, 3.4MB)

 Annual Groundwater Quality Survey 2020 (PDF, 6.1MB)

Risk maps of nitrate in groundwater

This report presents maps of the risk of nitrate contamination in groundwater and explains how we used our data to prepare these maps. Risk maps are updated when our groundwater monitoring data reveal regional scale changes in nitrate risk. 

Download the risk maps of nitrate in groundwater (PDF, 3.8MB).

Surface water reporting

Surface water is monitored at over 100 sites a month and the results are shown on the LAWA website.