Annual groundwater survey yet to show improvements in water quality
More E. coli detections and rising nitrate concentrations were found in Waitaha Canterbury groundwater last year.
Our annual groundwater quality survey report for 2024 has been released (PDF file, 3.4MB), with water samples from 349 wells across Waitaha sampled and analysed.
The wells tested are a mix of private domestic and irrigation supply wells, community water supply wells, wells for industrial supply, and purpose-built monitoring wells owned by us. The groundwater samples collected from these wells is from a range of depths and locations across the region.
What our survey found
E. coli was detected in 49 (14 percent) of the 349 samples, more than in 2023 (9 percent) but still in the range of what we have seen in previous years. Most E. coli detections were found in the shallowest wells – 38 of those detections were in wells less than 20m deep.
Nitrate-nitrogen concentrations ranged across the region, however, higher concentrations were found in areas around and downstream of intensive farming. Around 10 percent of wells were found to have nitrates above the Maximum Acceptable Value (MAV) for drinking water, a similar result to 2023.
Nitrate concentrations still increasing
In 2024, 301 of the wells we sampled had enough data to analyse trends over a 10-year period. Of these:
- 62 percent showed increasing trends in nitrate concentrations
- 18 percent showed no trend
- 20 percent showed decreasing trends in nitrate concentrations.
Chief Scientist Dr Elaine Moriarty said the annual sampling used in this report not only gives us a snapshot of groundwater quality in the Canterbury region, but provides data for evaluating long-term changes.
“Where we can see 10-year trends emerging, nitrate concentrations are increasing in many more sites than those showing decreasing trends,” Dr Moriarty said.
Mapping of nitrate-nitrogen samples by concentration shows that the Ashburton region had the highest nitrate concentrations, similar to previous years' surveys