Spring nitrates testing

What we are doing

We are testing the water in a spring on Bunz Steam, Te Kuru, for nitrate-nitrogen levels. Quarterly, starting September 2024, we take a water sample from this spring on Bunz Stream to Hills Lab which tests the sample for nitrate-nitrogen.

The results of our testing are recorded here as a longitudinal record for this site as a means of monitoring the quality of water entering the headwaters of the Ōpāwaho-Heathcote River Network.

Be aware that the Christchurch City Council conducts a comprehensive water quality testing programme along all principal waterways. Results of the CCC testing can be viewed here. The CCC testing point closest to this spring is Heathcote at Sutherlands Road. Test results at this point for nitrate-nitrogen are similar but not identical to our test results which is to be expected.

How much is too much?

Ecological health: The Australian and New Zealand Guidelines (ANZG) adopted in June, 2025 provide benchmark rather than a mandatory compliance standard values for nitrate toxicity in freshwater with protection bands that indicate a Level of Species Protection (LOSP). At the present time, the National Policy Statement for Freshwater Management 2020 (NPS-FM) provides the compulsory statutory regulations for New Zealand councils.

Band A: High conservation value system. Unlikely to be effects even on sensitive species. ≥99% LOSP
Band B: Some growth effect on up to 5% of species. ≥95% LOSP,
National Bottom Line. = 95% LOSP.
Band C: Growth effects on up to 20% of species (mainly sensitive species such as fish). No acute effects. ≥80% LOSP
Band D: Impacts on growth of multiple species, and starts approaching acute impact level (that is, risk of death) for sensitive species at higher concentrations (>20 mg/L). <80% LOSP

Drinking water: The Maximum Acceptable Value (MAV) has been set at a nitrate-nitrogen concentration of 11.3 mg/L. Some studies have suggested that there are human health risks at concentrations much lower than the MAV. A level between 0 and 1 mg/L is the optimum result for drinking water.

Test results

The graph shows all results to date (with tolerance levels of 0.002 mg/L for each test indicated) as well as a linear trend forecast over all the results since the testing began. Note: Trends are unreliable with small sample numbers.

mg/L

Lowest value

1.81

Highest value

2.30

Median value

2.15

Annual Median value

2.15

Nitrates in groundwater

Nitrate is the most widespread groundwater contaminant in the world, contributing to algal blooms and posing a human health hazard to drinking water. Nitrate can also threaten the ecological health of surface water bodies like streams, rivers and lakes. If groundwater has high nitrate-nitrogen concentrations, any surface water fed by groundwater springs will also have high concentrations.

How does nitrate enter groundwater?

Nitrate is highly soluble in water. As it forms in soil from the decay or oxidation of other nitrogen compounds, nitrate dissolves readily into the water in the soil pores. From there, plants can draw the nitrate in through their roots and use it to build proteins and amino acids that they need to grow. However, if there is more nitrate present than the plants can take up, the excess remains in the soil. Then, when it rains, that nitrate is washed, or leached, downward through the soil and into the underlying groundwater.

Therefore, nitrate contamination of groundwater occurs as a result of excess nitrate in the soil. This might be a result of excess application of fertiliser or farm effluent. It can also result from animal urine, human wastewater, or soil cultivation.

Does nitrate occur naturally in groundwater?

Nitrate is a natural chemical and it does occur naturally in groundwater, but generally at low concentrations. Estimates of natural nitrate-nitrogen concentrations in New Zealand groundwater range from as low as 0.25 mg/L to as high as 3.5 mg/L.

Click here to read about the ecological baseline survey of this spring

What is nitrate-nitrogen?

The term ‘nitrate-nitrogen’ refers to the nitrogen portion of the total nitrate in a sample. Nitrate is a common, naturally occurring chemical compound made of the elements nitrogen (N) and oxygen (O). It is an important source of the nitrogen that is essential for plants to grow. Nitrate is derived from the decay of organic material in soil and animal excrement, and it can also be manufactured as nitrogen fertiliser.

Elevated levels of nitrate are predominantly due to intensive dairy and cattle farming practices (high stock levels and fertiliser application). For a full explanation of nitrate-nitrogen in groundwater, read this Factsheet from LAWA.

Where is this spring on Bunz Stream?

The spring is on the edge of the Te Kuru retention basin system and is best accessed from the small footbridge on the bend in Bunz Road, before reaching Beamsgate Road.