Groundwater Quality

Groundwater is a vital resource for New Zealand. It is widely used as a source of drinking water, whether by individual households with their own wells in rural areas, or by communities and cities as large as Christchurch and Wellington. Groundwater is also used for irrigation and industry, and it feeds many streams and lakes. Understanding the quality of groundwater helps us to manage land uses that affect it and the uses that depend on it.

Pathogens, nitrate and other contaminants can affect the suitability of groundwater for various uses. Groundwater contaminants, especially nitrate and phosphorus, can also affect the quality of the spring-fed streams and lakes. In coastal areas, over-use of groundwater can draw seawater into the aquifers, rendering the groundwater unsuitable for drinking or irrigation.

Data collected by regional councils and unitary authorities shows that while most groundwater is of very good quality, contamination from E. coli and nitrate does occur. Regardless of where a well is located, all groundwater is potentially vulnerable to pathogen contamination (indicated by E. coli), so people should have their well water tested regularly. Nitrate concentrations exceed drinking-water standards in some wells, and long-term trends are variable, with roughly equal numbers of wells displaying improving and degrading trends. Seawater intrusion is not widespread, but continued monitoring is important so that we know if the situation changes.

On LAWA, you can see results for five groundwater quality indicators monitored by regional councils and unitary authorities:

• Nitrate-nitrogen is an important nutrient for plant growth, but at high concentrations it can threaten ecosystem and human health.
• Dissolved reactive phosphorus is another plant nutrient that can cause excessive weed and algae growth in lakes and streams.
• Chloride is an indicator of seawater contamination.
• Electrical conductivity is a general indicator of the total dissolved salts in the water.
• E. coli is an indicator of faecal contamination that can render the water unfit for drinking without treatment.

Council groundwater quality monitoring programmes are designed to capture environmental state and trend on a regional scale, so it’s important not to place too much emphasis on the results from an individual well. Looking at an individual well gives you a picture of how indicator values change over time, but in most cases, we do not have enough information about the specific, local factors influencing an individual well to identify all the drivers of change.

The data is most useful at a regional scale. Use the map, zooming in to a water management zone or out to the entire country, to look at patterns of where parameter values are high or low, or where they are increasing or decreasing. Explore the rich data set that councils have compiled of years of monitoring, and learn more about New Zealand’s precious groundwater resources.

Ministry for the Environment (MfE) and Stats NZ regularly report on New Zealand’s freshwater resources. Our freshwater 2020 is the latest in a series of environmental reports produced by the Ministry for the Environment and Stats NZ, and includes a national level overview of groundwater quality. The report uses some of the data presented here.