E. coli and nitrate found in some Canterbury groundwater
Environment Canterbury media release: 13th May 2024
More than half of wells monitored in our annual well survey showed nitrate levels still likely increasing.
The results of our annual groundwater survey of 349 wells across Canterbury show little change, with high nitrate levels and E. coli detected in some water sources.
We tested a range of water quality measures from water samples for our annual survey. Sample were taken from a mix of private domestic wells, irrigation water wells, community water supply wells, wells for industrial supply, and purpose-built monitoring wells.
E. coli was detected in 32 water sources - slightly fewer than the previous year’s survey.
Some 35 water samples showed nitrate-nitrogen concentrations above the Maximum Acceptable Value (MAV) of 11.3 mg/l - down from 44 in 2022. However, nitrate levels appear to be increasing in 59 per cent of the wells surveyed, with only 17 percent likely decreasing.
Results similar to previous years' findings
Acting Groundwater Science Manager Davina McNickel said that the 2023 results are in line with what we’ve found in previous years.
“Groundwater quality results do not show any clear improvement or reversal of increasing trends in nitrate concentrations,” McNickel said.
“Efforts to change land use and farming practices over the past 10 years were designed to reduce nitrogen concentrations in our groundwater,” she added. “However, it will take many years before we start to see reductions in nitrate in groundwater as a result of these efforts.”
“We also test for E. coli because it is an indicator of faecal contamination,” McNickel said.
“Like last year, around nine per cent of the wells we sampled contained E. coli. Our groundwater is vulnerable to contamination from faecal sources, and we recommend that people who own private wells test regularly for the presence of E. coli, especially after heavy rain.”
Download the Annual Groundwater Quality Survey 2023.
Find out more about drinking water in Canterbury.
Learn more about farming rules and practices to reduce nitrogen loss (ECan Farmers' Hub).