Some private bores in the Waimea Plains may have nitrate-nitrogen levels which exceed the NZ Drinking Water Standards. If you are drinking water from a private bore, it is important that you consider having your water tested. If the nitrate-nitrogen levels exceed those set in the standards, you should seek further advice(external link).
One of the key challenges in the Waimea catchments is the level of nitrate-nitrogen (NO3-N) in groundwater beneath the Waimea Plains. In some areas, nitrate levels in the aquifers are elevated, and test results from some bores and wells exceed the New Zealand Drinking Water Standards for nitrate (11.3 mg/L).
Excess levels of nitrate in groundwater may affect the ecology of spring-fed streams. It may also affect the suitability of water for some growing operations (for example it can impact keeping apples in cool-storage). Consuming water with concentrations higher than the current drinking water standards may also affect human health.
Historical monitoring of water taken from bores across the Waimea Plains has long shown elevated levels of nitrate-nitrogen, and there have been some improvements over time. Recent monitoring has revealed nitrate levels higher than the current drinking water standard. Anyone using a private bore or well for drinking water needs to be aware of the situation so they can make informed decisions.
Note, the nitrate levels in Richmond’s public water supply remain slightly less than half the NZ Drinking Water Standards.
Council is actively working to better understand the cause of high nitrate levels and possible remedies. Growers on the Waimea Plains produce the bulk of our region’s horticultural produce, and we are establishing processes to work constructively with them to reduce nitrogen use and loss over time.
As a Council, we take our responsibility for local water quality seriously and have recently employed a full-time soil scientist to accelerate this work. We are also developing a Plan Change and Action Plan to address this issue, and there is more to be done by farmers, industry, and Council in coming years. Groundwater systems can be slow to respond to change and it is likely we will see elevated nitrate levels for some time to come.
The sections below outline the current advice on:
Nitrate (NO3) is a common, naturally occurring chemical compound made of nitrogen (N) and oxygen (O). It is an important source of the nitrogen that is essential for plants to grow. The nitrogen in nitrate comes from the decay of organic (animal and plant) material in soil, some plants collect it from the air, and it can also be manufactured as nitrogen fertiliser.
Land uses such as farming and sewage disposal systems release nitrate to the soil. When soil contains more nitrate-nitrogen than plants can use, the excess can be washed downward by rainwater and carried into the underlying groundwater. Nitrate levels are generally highest in shallow groundwater aquifers.
Excess nitrate can be a problem for human and ecological health. Too much nitrate in groundwater that feeds spring-fed streams can cause undesirable weed growth, algal blooms, and toxicity for fish and invertebrates. If groundwater with high concentrations of nitrate-nitrogen is used as a source of drinking water, it can pose a risk to human health.
Nitrogen is essential for all living things, but high levels of nitrates may have adverse health effects. Humans consume nitrate through food. For most adults, most of the daily nitrate intake comes primarily from vegetables, some from cured meats, and there are also small amounts in fish and dairy products.
Nitrate-nitrogen plays an important role in the terrestrial nitrogen cycle. Learn more about this on the Science Learning Hub website.
Groundwater is water found beneath the ground surface. When it rains, some of the rain water soaks into the soil and percolates downward into the ground. It fills cracks in rocks and pore spaces between grains of sand and gravel until the ground is saturated, creating an underground body of water known as an aquifer.
There are vast quantities of water in aquifers beneath the ground surface, slowly flowing and seeping through all those cracks and pore spaces. When we dig or drill a well, we can intercept some of that water and pump it out of the ground to use for drinking water supply or irrigation.
Find out more on LAWA: www.lawa.org.nz/learn/factsheets/groundwater/groundwater-basics.
Waimea groundwater has historically had elevated nitrate concentrations. This has largely been attributed to a large-scale piggery operation in the Hope area many years ago, as well as land use impacts from across the plains. The nitrate contamination from the historic piggery has been decreasing over the last few decades.
In recent years, groundwater sampling has identified an area around Ranzau Road (West) through Bartlett Road, in both the Upper Confined Aquifer and the Appleby Gravel Unconfined Aquifer, where higher than expected nitrate concentrations have been determined. The nitrate concentrations are well above the NZ drinking water standard of 11.3 g/m³-N and similar to those encountered 20 to 30 years ago.
Ecologically, we’re not detecting any obvious impact on surface water quality or our spring feed creeks over and above what we have seen historically.
Between October and December 2021, a water quality survey was undertaken in the Waimea Plains. This is the sixth and most recent water quality survey undertaken in the plains.
Of the 137 bores/wells sampled in the Waimea Plains, 56 sites (41%) had nitrate-N below 50% of the MAV (below 5.6 g/m3-N), 42 sites (31%) were between 50% of the MAV and the MAV (between 5.6 and 11.3 g/m3-N), and 39 sites (28%) were above the MAV (above 11.3 g/m3-N).
The highest nitrate-N concentrations in 2021 were found at the intersection of Bartlett Road/Ranzau Road West (31 g/m3-N) and along Blackbyre Road (30 g/m3-N). All bores/wells sampled between these two locations exceeded the MAV for nitrate-N. The area between Bartlett Road and State Highway 60 is where the UCA and the AGUA merges together and becomes hydraulically indistinguishable. Any discharge of nitrate-N from the UCA would be noticed here and would be contributing to the elevated nitrate-N concentrations at the Bartlett Road/Ranzau Road West intersection. Blackbyre Road is outside of the UCA reach, however water from Bartlett Road is likely to travel towards Blackbyre Road as the flow of groundwater progresses towards the coast.
Unconfined groundwater south of Brightwater shows most sites sampled being well below 50% of the MAV. North of Brightwater on both sides of the Waimea River, nitrate-N was near or above 50% of the MAV. East of the Waimea River and east of Burkes Bank, the majority of all four aquifers were near or above the MAV. West of the Waimea River, bores/wells in the AGUA along Cotterell Road/Moutere Highway/River Road/Waimea West Road were also near or above 50% of the MAV. It was anticipated that these areas would have higher concentrations of nitrate-N due to the overlying horticultural and agricultural activities.
The large number of samples where nitrate-N concentrations are near/above 50% of the MAV across the main horticultural and agricultural areas on the Plains shows that input from present-day activities are contributing to nitrate-N entering in the groundwater in all four aquifers.
Read the full Technical Report Waimea Groundwater Quality Survey 2021 (pdf 11 MB)
In 2020, Council commissioned a review and summary of the available science on the nitrate issue in Waimea aquifers and related land use to provide a picture of what we know so far. Below are some of the points highlighted in the report:
Health risks around nitrate are complex. Health risks arise from our bodies changing nitrate into other nitrogen compounds that can potentially affect our health. These bodily processes can also be affected by our diets, the quality of our drinking water supplies (e.g. whether they also include bacteria that can cause illness), and our current health and age. Dietary influences include how much nitrate we ingest, for how long, and how many protective factors – for example antioxidants found in vegetables - we consume that help to prevent the formation of health-affecting compounds.
The drinking water standards for nitrate are currently set at a maximum allowable limit of 11.3 mg/L. Consuming water with concentrations of nitrate-nitrogen higher than the current drinking water standards poses a health risk, particularly to babies. If your drinking water is above the current drinking water standard, you should not drink the water if you are pregnant, and should not give the water or use it to prepare food for babies as they are at risk of methemoglobinemia, also known as blue baby syndrome. Boiling water before drinking or preparing formula does not remove nitrates.
Recent research has raised new concerns about possible health implications from drinking water with high levels of nitrate-nitrogen. The Ministry of Health continues to review emerging evidence and research to better understand if there is a link between adverse health and nitrates in drinking-water at levels lower than the current maximum acceptable value (MAV). Updates on where the Ministry is at in this process are available on the Ministry of Health website and and a useful summary on nitrates in drinking water is available from the Prime Minister’s Chief Science Advisor.
Council aims to manage publicly owned water supplies to meet the NZ Drinking Water Standards and advises affected communities where public supplies do not meet the standards. For private community water supplies and individually owned bores and wells, the owner is responsible for ensuring water (at the tap) meets the NZ Drinking Water Standards.
Levels of nitrate in groundwater vary a lot across the Tasman District. Most groundwater in the district is well below the current drinking water standards and the Council's reticulated water systems are managed to minimise nitrates. Groundwater in some areas below the Waimea Plains can exceed the NZ drinking water standard and many households and businesses on the Waimea Plains are not connected to ‘mains’ reticulated water supplies. Some of these households and businesses may use private bores for their drinking water supplies.
Current Ministry of Health advice is that people who may be at risk of health effects from elevated nitrate in drinking water or water used for food preparation include:
Ministry of Health advice for people who may be at risk of elevated nitrate in drinking water is that if your drinking water is at a level exceeding health limits (>11.3mg/L Nitrate-N), find an alternative water source, use bottled water, or investigate effective treatment options.
A map of the areas potentially at risk of elevated nitrates in bores and well water is available: Download a copy here (pdf 2.3 MB).
If you have any questions about your drinking water bore or supply, you can contact Tasman District Council Environmental Health Officers on 03 543 8400.
If you are concerned about a medical condition, you should contact your usual health provider or in an emergency, dial 111.
The Ministry of Health has released it's own guidance on nitrates in drinking water. You can read that here.
Their website has more information, including specific advice on how to ensure your bore or well is secure, as well as information on water supply treatment options.
Council continues to work with the Nelson-Marlborough DHB and we will share any further public health guidance from the Ministry of Health.
Council’s reticulated water supply is not adversely impacted by elevated nitrate concentrations on the Waimea Plains and complies with the NZ drinking water standard. Rainwater collected from the roofs of buildings is also not affected by nitrate contamination in the aquifers.
In New Zealand, households not connected to the mains are responsible for monitoring their own bore water. Testing is the only way to detect nitrate as it is tasteless, odourless, and colourless. If you live in an area with elevated nitrate levels and you use groundwater as your drinking water source, you should consider getting your drinking water tested regularly.
Nitrate levels vary over the year. Sometimes we see higher levels following heavy rain events, though this depends on other factors also. One sample may not be representative of your typical levels but if your water is high in nitrate, contamination is occurring. Nitrate levels in groundwater are generally highest in spring. Therefore, we recommend if you test annually, to do this during the spring months to get an indication of whether you have elevated levels.
There are many laboratories that can test for nitrate in a water sample. The laboratory must be contacted first because they provide special sampling containers, protocols for collecting the sample, and recommendations. Visit the IANZ website directory and search for nitrate to get a list of accredited laboratories that offer testing.
The Drinking Water Standards give a Maximum Acceptable Value (MAV) of 50mg/L for nitrate (measures both nitrogen and oxygen in the nitrate), which is equivalent to 11.3mg/L nitrate-N (measures only the nitrogen in the nitrate). Check with your laboratory for result interpretation as it is easy to mix up the two different units.
If you are renting or leasing land and not sure where your drinking water is coming from, check with your landlord. In Tasman, some buildings get drinking water from the mains system, others get their drinking water from groundwater or rainwater, and some are a mix of rainwater supplemented with groundwater.
Check that your bore or well is not located within at least 20 metres of any potential sources of nitrate, such as an onsite wastewater system, chicken coops, stock holding areas, or fertiliser or manure storage. In some cases, nitrates in bores or wells comes from a local source, rather than general land use effects. Wells can be more susceptible to contamination than bores as they are shallower and more vulnerable to surface run-off. It’s also important to check your well head is fully secure to ensure surface drainage cannot get in. Learn more.
Nitrate is difficult to remove from water. Reverse osmosis and ion exchange can remove nitrate however these are expensive options (contact your local pump and water filter supply store for options and costings). Household cartridge, carbon filters, chemical treatment, and boiling will not remove nitrate effectively.
Alternative sources to groundwater include:
The Ministry of Health has more information on drinking water sources here.
Some of these alternatives may require resource or building consent or engineering approvals. For further information on requirements, contact Council on 03 543 8400.
These are complex issues and groundwater systems can be slow to respond to change. It may take years for us to see the effects of changes that are made now, by growers, Council, and others.
Council recognises this is an important issue that needs to be addressed. Additional staff have been recruited for technical (soil scientist) and planning positions to help. We are actively working to better understand the cause of high nitrate levels and possible remedies. The most appropriate means of controlling nitrate concentrations, particularly in groundwater, is the prevention of contamination. This may take the form of appropriate management of agricultural practices (e.g. management of fertiliser and cropping practices) and sanitation practices (e.g. the careful siting of onsite wastewater e.g., septic tanks).
The context of land and water management has also changed significantly in recent years. We have new and anticipated legislation, changing market and community expectations, and increasing grower awareness and improving practices. The Government’s Essential Freshwater Package introduced nitrogen caps and fertiliser use record-keeping for some land uses. It will also set up regulations that will require landowners to have Freshwater Farm Plans that show how nutrients are managed on the property.
Growers on the Waimea Plains produce the bulk of our District’s horticultural produce. In November 2020 we held a workshop with Waimea plains landowners and growers to discuss the Waimea nitrate science summary and begin discussions to identify on-farm options for management of nitrates. The aim of this work is to support growers to achieve effective practices in nutrient management and to ensure any nitrate leaching is minimised over the next year and onwards. This is in preparation for the national roll-out of the Freshwater Farm Plans regulations.
The current Tasman Resource Management Plan has limited rules controlling nitrate discharges and land use. However, the plan is currently undergoing a review to implement the National Policy Statement for Freshwater Management 2020. This will ultimately result in new resource management policies and rules. The new plan named Aorere ki uta, Aorere ki tai - Tasman Environment Plan will include new policies and rules covering land and water, use and management. You can keep up to date with progress and get involved in its development here: www.environmentplan.tasman.govt.nz.
Following changes to the RMA in June 2020, any water-related plan changes must use a special five-member hearing panel and in light of this we are seeking to minimise the number of individual plan change processes for freshwater. The Waimea Plains plan change will now likely occur within our whole-of-plan review process (www.environmentplan.tasman.govt.nz) rather than as a separate plan change. This will also allow time for iwi and community input into discussion on what values the Waimea River and aquifers are managed for and how best to achieve desired outcomes. These discussions will occur over the next year.
In the meantime, Council's soil scientists and policy staff will be working with industry and growers to identify risks to water from nitrate leaching and practical approaches to minimise any leaching or run-off.
Overview of nitrates in drinking water from the Prime Minister's Chief Science Advisor
Nitrate in drinking water (Ministry of Health)
Drinking Water (Ministry of Health)
Drinking-water Standards for New Zealand (Ministry of Health)
Drinking Water in New Zealand (ESR)
Guidelines for drinking-water quality 4th ed. (World Health Organisation)
Secure Groundwater Bores and Wells for Safe Household Water (HealthEd)
