Maximum amount of nitrate that is acceptable in drinking water
Find out about the maximum acceptable value (MAV) of nitrate listed in NZ's Drinking Water Standards and about MAVs more generally.
As the country’s water services regulator, Taumata Arowai wants to ensure that safe drinking water is available for everyone in Aotearoa New Zealand, every day. New Zealand’s Drinking Water Standardsoutbound set out the maximum amount of nitrate and other substances that are acceptable in drinking water. In the public health and water sectors, these maximum amounts are known as the “maximum acceptable value” or “MAV’.
The maximum amount of nitrate acceptable in drinking water under New Zealand’s Drinking Water Standards is 50 milligrams per litre. See below for further information.
There are a number of ways that people can consume nitrate. Drinking water is just one of these. For example, nitrate can be found in processed meats and other foods. However, a range of factors impact how the body absorbs nitrate.
How MAVs are set
New Zealand’s MAVs are generally based on World Health Organisation drinking water guideline values, which are based on the body of scientific evidence that is available internationally.
The Ministry of Health - Manatū Hauora provides advice to Taumata Arowai on matters concerning New Zealand’s MAVs and related public health policy.
Based on the available health evidence, the Ministry of Health considers the current MAV for nitrate to be appropriate. The Ministry continues to monitor and review the overall body of evidence on nitrate in drinking water.
New Zealand’s MAV for nitrate is consistent with Australia and countries in the European Union.
How does a drinking water supplier know if their water meets the MAV?
Registered drinking water suppliers are required to regularly test their drinking water for a range of substances, including nitrate.
Both the drinking water supplier and the accredited laboratory used for the testing must then notify Taumata Arowai if any results over the MAV are found, and suppliers must take immediate action that’s needed to protect public health.
Taumata Arowai informs the Regional Public Health Service when testing results exceed a MAV, when appropriate. Taumata Arowai can take action if we consider that a supplier is not adequately responding to a situation where the MAV has been exceeded.
If a member of the public has any questions or concerns regarding their drinking water, they should contact their drinking water supplier.
More information
Information from other agencies
- Nitrates in drinking water | Office of the Prime Minister’s Chief Science Advisoroutbound
- Addressing risks associated with nitrates in drinking water | Ministry for the Environmentoutbound
Are there two MAVs for nitrate?
There is just one maximum amount of nitrate that is acceptable in drinking water.
However, the MAV for nitrate is unique as it includes two different ways to express how much nitrate is in water. This is because there are two different ways to measure this.
In chemistry, a nitrate molecule is NO3. This means it’s made up of one nitrogen atom and three oxygen atoms.
The amount of nitrate in water can be expressed in two ways:
| If the following is being measured… | …you’ll see this is written as… | …and the maximum amount acceptable under NZ’s Drinking Water Standards is… |
|
both the nitrogen and oxygen atoms that make up a nitrate molecule
|
nitrate or NO3 |
50 milligrams per litre of water |
|
just the nitrogen atoms that make up a nitrate molecule
|
nitrate-nitrogen or NO3-N
|
11.3 milligrams per litre of water |
However, no matter what approach is used, the maximum amount of nitrate acceptable in drinking water is the same.
The ratio of nitrate to nitrite (NO2) in drinking water is also important. New Zealand’s Drinking Water Standards include a maximum for this ratio.
How often does a drinking water supplier need to test water for nitrate?
How often a drinking water supplier must test for nitrate depends on the size of the community that a supply serves.
For small drinking water supplies (serving 26-100 people), source water must be tested for nitrate every three years. If a result exceeds 50% of MAV, water must be tested every three months.
For medium supplies (serving 101-500 people), source water must be tested for nitrate annually. If a result exceeds 50% of the MAV, water must be tested every three months.
For large supplies (serving more than 500 people), source water must be tested for nitrate every month.
In summary, when sampling in small and medium supplies indicates a result that exceeds 50% of MAV, sampling must take place every three months until six consecutive test results are less than 50% of the MAV. Large supplies must always test for nitrate monthly.