Annual groundwater quality survey shows little change

Environment Canterbury released its annual groundwater quality survey for 2018. While public drinking water supplies are safe, it confirms that a few private wells are sometimes below drinking water standards.

The report summarises the current state of groundwater quality throughout the region and provides analysis of trends over the past decade.

Groundwater Science Manager Carl Hanson said each spring, when groundwater levels are usually highest, Environment Canterbury collects samples from wells to help understand the state of the resource and assess changes in water quality over time.

“The data in the latest report is what we expected,” he said. “The results are similar to most years, noting that these are ‘snapshot’ surveys.

Protecting our groundwater

“Groundwater is vulnerable to contamination, including E coli and nitrates. For the 2018 survey, 306 wells were sampled region wide. Thirty- four of these (11%) had E.coli and 22 (7%) had nitrate above the Maximum Acceptable Value (MAV).”

MAV is the national drinking water standard, set at 50 milligrams per litre for nitrate, equivalent to 11.3 milligrams per litre of nitrate-nitrogen.

Carl Hanson said all wells with nitrate and E.coli above MAV were private wells. “Most are not used for drinking water. All these well owners have been notified. Some have installed filters if they are drinking the water. Others have replaced the wells, but we still monitor old wells for our long-term trend analyses.”

Nitrate concentrations in groundwater are increasing due largely to the lag effect of many years of agricultural and other land uses.

“In recent times we have seen a reduction in the rate of increase,” Carl Hanson said. 

Farming rules

“Environment Canterbury takes nitrate levels very seriously. Canterbury has some of the strictest land-use rules in New Zealand to protect the region’s water quality.

“Farmers must adhere to strict water quality limits, obtain consents to farm, and implement good management practices. Stock exclusion rules are in place. Fences and buffer strips are encouraged at the edges of rivers and streams to prevent animal waste entering the water.

“All these steps will ensure that over time less nitrate will enter Canterbury’s water. This is taking time, but it is happening.”

Private drinking wells

While Environment Canterbury is responsible for the health of all groundwater and surface water in the region, people with private drinking wells have responsibility for ensuring they have a safe supply.

Carl Hanson offers this advice: “Make sure your well is secure and test your water periodically. In most cases, samples can be taken from a kitchen tap and sent to a lab for testing at your own expense.”

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