Nitrate in drinking-water

This webpage tells you how to find out if nitrate is in your drinking-water and, if it is, what to do to keep yourself and your family safe from any harmful effects.

What is nitrate?

Nitrate is a naturally occurring organic compound that contains oxygen and nitrogen atoms. It can be found in low concentrations in water and soil. Nitrate is vital for a healthy environment. Nitrate has no detectable colour, taste, or smell in drinking-water.

Nitrate in drinking-water

If your drinking-water comes from a private bore then nitrate may be present in it. You are responsible for testing your bore water to ensure it is safe.

If your drinking-water comes from rainwater then you do not need to be concerned about nitrates. Find out how to keep your rainwater safe in ESR's Household water supplies manual.

If your drinking-water comes from a council or community water supply then the supplier is responsible for monitoring the water. They must test for nitrates if they have been found to be present at levels above 25 mg/L in the past.

Potential effects of high nitrate levels in drinking-water

Using drinking-water that has nitrate levels above 50 mg/L can cause methemoglobinemia (blue-baby syndrome) in bottle-fed infants. Children under six months are most vulnerable.

Nitrate can be reduced to nitrite in the gut of an infant. It is then absorbed into the blood where it interferes with oxygen transfer. This gives the infant a blue colour, especially around the eyes, lips, and fingers. Other symptoms of blue-baby syndrome include headache, tiredness, and shortness of breath.

An infant with blueish skin should be taken to a doctor immediately.

There is a higher risk of blue-baby syndrome if the infant has a stomach bug. To reduce the risk of illness, you must make sure that drinking-water used for infants is free from harmful bacteria and viruses. Until your baby is at least 18 months old, all bore water used for formula should be boiled and cooled to room temperature on the day you use it. This will kill harmful bacteria and viruses – but will not remove any nitrates.

If you are pregnant, high nitrate levels may reduce the amount of oxygen getting to your baby.

Testing drinking-water for nitrate

You will need to collect a sample of your drinking-water and send it to an accredited laboratory for testing. You can get a testing kit and instructions on how to take samples from the laboratory. Your local public health unit can give you details for the nearest laboratory, or search the full list of accredited laboratories in New Zealand.

You should regularly test your water for nitrates because levels change frequently – at least once per year.

What to do if your drinking-water is high in nitrate

Pregnant people and infants under six months old should not drink water that has a nitrate level above 50 mg/L.

If a test shows that the nitrate level in your bore water is close to or above 50 mg/L you need to treat the water or use another water source. Common methods such as boiling and disinfection do not remove nitrates.

Point-of-use devices

A small treatment unit called a "point-of-use device" can be installed under your kitchen tap to remove nitrates. Ion exchange and reverse osmosis are the best point-of-use devices for removing nitrates from drinking-water.

  • Ion exchange devices pass your water through a tank filled with resin that absorbs the nitrate, providing water with over 90 percent of nitrates removed. 
  • Reverse osmosis uses pressure to force water through a filter that removes most of the nitrates.
  • Get more information about these devices in ESR's Household water supplies manual.

These devices are expensive, so you should first consider if there is a better alternative water source for you to use. Bear in mind how long the device will operate before parts need replacing and how much that will cost. Equipment manufacturers and suppliers can tell you how long the equipment will last and how to keep it working effectively. 

How nitrate gets into drinking-water

Nitrate dissolves in water which makes it easy to transport through soil to groundwater. It can enter surface water or groundwater as runoff from domestic, agricultural and industrial sources. This is called contamination. Sources of contamination include:

  • decomposing plants
  • excess fertiliser
  • animal waste
  • wastewater
  • septic tanks.

Preventing nitrate from entering your drinking-water

The safest groundwater comes from confined aquifers under areas that have little access by people or animals and where there is no intensive agriculture or industry. This is not always possible so it’s very important to take all necessary steps to prevent contamination. You should:

  • construct your bore in a safe location
  • dig a deeper bore to access a confined aquifer (if possible)
  • seal and protect your bore from contamination
  • regularly inspect your bore for damage
  • keep nitrate sources away from your bore.

Find more information about protecting your bore from contamination in HealthEd's pamphlet Secure Groundwater Bores and Wells for Safe Household Water.

What the Ministry of Health is doing

The Ministry of Health continues to review new evidence and research about nitrates in drinking-water to understand links to adverse health. Current evidence suggests that nitrate levels lower than 50mg/L are safe.

Our drinking-water regulator, Taumata Arowai

Taumata Arowai will take over as the drinking-water regulator for Aotearoa when the Water Services Act comes into effect in late 2021. Taumata Arowai will require all water supplies to monitor for nitrate (and other chemicals) in their first year of operation.

The Ministry for the Environment

An efficient way to prevent drinking-water contamination from nitrates is by protecting source waters. To achieve this the Ministry for the Environment (MfE) is amending the National Environmental Standard for Sources of Human Drinking Water (NES-DW). These amendments will prevent contamination of water sources in the first place by managing the risks from surrounding land uses and activities. This will improve water quality in general and for human consumption.

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