As part of the review of the National Environmental Standard for Sources of Human Drinking Water, the Ministry for the Environment commissioned a report on the potential impacts of national implementation of drinking water source protection zones. Aqualinc won the project through a competitive tender process.

We identified, from the New Zealand drinking water register, all drinking water sources that serve more than 100 people.

For both groundwater and surface water sources, we delineated source protection zones using methods that had been defined previously by others. A range of methods are available for delineating source protection zones: we selected the most detailed methods possible, given the level of input data that could reasonably be assembled at a national scale. For groundwater sources we delineated a protection zone, based on a one-year contaminant travel time, and a larger capture zone, based on a 50-year travel time. For surface water, we identified both an intermediate zone, extending 25 km upstream and 100 m landward, and the entire catchment area upstream of the source.

Using national-scale datasets and a database of resource consents that we compiled from regional council data, we assessed the impact on current land uses and consented activities. We developed a risk-based framework to assess the relative costs of implementing source protection zones.

The project also included an assessment of regional council planning rules relating to drinking water source protection.

Assembling the datasets required for an assessment on a national scale was a challenge due to inconsistencies in the format in which regional councils hold their resource consent data.

The availability of groundwater data on a national scale (hydraulic properties and land–surface recharge, for example) limited the accuracy with which groundwater source protection zones could be defined.

We created a number of spatial datasets (shapefiles) of the water sources, the source protection zones, resource consents on a national scale, and the land cover within the source protection zones.

The current land cover within the groundwater protection zones is predominantly high-producing grassland. Most of the surface water intermediate zones’ land cover was assessed as being low risk for water quality. The spatial variation in affected areas and affected land cover types indicate that the impact of implementing a national standard for source protection zones would also vary regionally.

The challenges in completing this analysis on a national scale, due to the different approaches taken by different regional councils and the level of information available, highlight that nationally consistent implementation of drinking water source protection zones will be a challenge.

The methodology and results were summarised in a report, which is available on the Ministry for the Environment’s website.