Factsheet: Monitoring groundwater in New Zealand

Why monitor groundwater?

Groundwater changes over time. Groundwater levels rise and fall as the seasons change, and in response to heavy rainfall and groundwater use. Groundwater quality can also respond to changes in the seasons and to rainfall events, as well as to changes in land use. By monitoring groundwater, regional councils and unitary authorities can track and understand these changes.  This information is helpful for resource management.

How is groundwater monitored?

Council staff regularly visit wells across each region to measure water levels and collect groundwater samples. They identify a set of wells that together gives a regional-scale picture of groundwater resources, and they return to those wells over and over, on a regular frequency, to build a long-term picture of changes to the groundwater system.

Groundwater quality is monitored by regularly collecting groundwater samples from wells. Regional council staff collect samples following the National Environmental Monitoring Standards (NEMS) for groundwater quality data, and samples are sent to accredited laboratories for analysis. Each well may be sampled annually, quarterly or monthly depending on the purpose of the monitoring.

The groundwater level in a well can be measured manually by dipping a graduated tape down the well. Councils typically make these manual measurements monthly. Alternatively, a variety of automated sensors can be installed in wells to monitor water levels continuously. Some of these sensors can transmit the data back to the council offices in real time.  These 'real-time' data can be viewed in the LAWA Water Quantity topic.

Councils use a variety of wells in their monitoring programmes. Some are purpose-built monitoring wells, and others are public or community water supply wells, but the majority are privately-owned wells used for domestic or stock-water supply, irrigation, or industry. Councils would like to thank the owners for allowing their staff access those wells and collect the monitoring data that is so important to managing New Zealand’s groundwater resources.

Regional and national monitoring programmes

Groundwater quality is monitored at the regional level as part of council State of the Environment (SOE) monitoring programmes. At a national level, regional authorities collaborate with GNS Science as part of the National Groundwater Monitoring Programme, or NGMP.  This long-term research and monitoring programme involves sample collections across New Zealand by council staff following standard protocols, and analysis by the GNS Science laboratory.  LAWA presents data from the NGMP as well as from wider council monitoring programmes.

How is groundwater monitoring data used?

Groundwater quantity and quality monitoring is reported by each region as part of its State of the Environment (SOE) reporting. The frequency of reporting varies between regions. On a national scale, the Ministry for the Environment uses council monitoring data in their environmental reporting programme. These reports are used to inform freshwater management policies and plans.

What groundwater quality indicators are analysed?

The sampling suite varies somewhat between councils depending on the objectives of the monitoring.  LAWA presents results for five groundwater quality indicatorsE. coli is a type of bacteria used as an indicator of faecal contamination that would make the water unsuitable for drinking without treatment. Nitrate-nitrogen and dissolved reactive phosphorus are nutrients that can affect water quality in spring-fed streams. Nitrate-nitrogen can also affect human health at elevated concentrations. Chloride and electrical conductivity are primarily used as indicators of seawater contamination caused by excessive pumping of groundwater in coastal areas; they can also provide information on the age of the groundwater.

What does the monitoring tell us?

The results from regional council groundwater monitoring are best interpreted at a regional scale. At a local scale, groundwater flow is complex, and there are many potential factors that can affect the quality and quantity of water from an individual well. However, when the results from many wells are viewed together, they can tell us a great deal about how groundwater is changing at a regional scale.

On LAWA, the results are used to evaluate the state of the groundwater and to identify long-term trends in groundwater quality.