Nitrate in drinking water

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.

Using drinking water that has nitrate levels above 50 mg/L can cause methemoglobinemia (blue-baby syndrome) in bottle-fed infants. Pēpi (babies) under 6 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 healthcare provider 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 pēpi 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.

Feeding your baby infant formula — HealthEd (external link)

For more advice on blue-baby syndrome call Healthline free on 0800 611 116

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

If your drinking water comes from a private bore you are responsible for testing your bore water to make sure it is safe.

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 Aotearoa New Zealand.

Search for an accredited facility — IANZ (external link)

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

If your drinking water comes from rainwater then you do not need to be concerned about nitrates. Find out more about how to keep your rainwater safe on the ESR website.

Selection, operation, and maintenance of individual household water supplies — ESR (external link)

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.

Pregnant people and pēpi under 6 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 on the ESR website. 

Selection, operation, and maintenance of individual household water supplies — ESR (external link)

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. 

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.

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.