Nitrate exceedance in council drinking water supply near Waimate

A council-run rural water supply near Waimate has recently been impacted by high nitrate concentrations and is not meeting drinking water standards.

Environment Canterbury is supporting Waimate District Council to help resolve the nitrate exceedance at its Lower Waihao Rural Water Supply in the Glenavy and Morven area with technical advice and additional monitoring of land use activities in the area. Waimate District Council is providing alternative water via tankers for the 615 people impacted and communicating with scheme users on this issue.

Nitrate exists naturally in soil from the breakdown of organic matter and is also added through animal urine and fertilizer that has dissolved and has not been absorbed by the plants. If nitrate transfers into a water supply and is above 11.3 mg/L, the water will not meet drinking water standards for health.

Our role in drinking water

Our role as a regional council is to monitor surface water and groundwater across the region and to regulate activities that might affect water quality.

The monitoring and provision of the drinking water sits with the scheme supplier (in this case Waimate District Council).

Drinking water standards are the responsibility of Taumata Arowai.

Huge rainfall likely to be a contributor

It is likely that severe weather conditions – prolonged rain and flooding on 19-20 July 2022 –contributed to the particularly high nitrate concentrations observed in the well.

The heavy rain caused excess nitrate in the soil to get ‘flushed’ down to the groundwater flows. We are seeing sharp increases in nitrate concentrations in many of our monitoring wells across the region this spring, and we have seen similar increases after wet winters in the past.

Because the Lower Waihao supply is a shallow groundwater well, located in an area of intensive farming, it was particularly impacted. Our monitoring has shown nitrate concentrations in shallow groundwater in the area to be increasing over the past 20 to 30 years.

This was a driver for the setting of limits for nitrate losses that we now have in the Canterbury Land and Water Regional Plan.

Helping to resolve the problem

We have rules and nutrient limits in place for landowners in the area, as part of our Land and Water Regional Plan. Our zone delivery team has checked land use in the immediate catchment and, to date, we are unaware of any specific non-compliant land use activity in the immediate catchment.

Our land management advisors are working directly with farmers offering free advice and support on best practice farming to reduce environmental impacts and, in this catchment, there is a strong focus on supporting the introduction of new nitrogen fertiliser rules, which further restrict the amount of synthetic nitrogen fertiliser that can be applied to pastoral land.

We continue to meet frequently and work closely with Waimate District Council and we are providing technical advice to help inform its next steps relating to improving the water supply and designing a denitrification plant.

We are also reminding people with private drinking wells or bores to test their water to ensure their supply is safe.

Tighter farming rules to reduce nitrate concentrations

We know that nitrate concentrations are still increasing in this catchment and other parts of Canterbury – our groundwater monitoring shows this in regular reports which are publicly available. That’s why our rules are already in place to regulate nitrate in our freshwater – and stricter measures are being introduced.

We check, encourage and support good management practices, such as fencing off waterways from stock and planting along stream margins, through auditable Farm Environment Plans.

The National Policy Statement for Freshwater Management requires that freshwater quality is at least maintained, or ideally improved. This will require farmers to take even more action to reduce nitrate beyond current limits and provide for a stricter framework to measure synthetic nitrate’s application to land.

Nitrate exceedance at Pareora township near Timaru

The Pareora township water supply, run by Timaru District Council, has also recently recorded nitrate exceedances above the drinking water standards. Like Lower Waihao, this exceedance is also believed to be exacerbated by the July 2022 weather event.

Nitrate concentrations in this supply have now improved and are within the maximum allowable value for drinking water standards.

The role of Community Drinking Water Protection Zones

Both the Pareora and Lower Waihao supplies are located within Community Drinking-water Protection Zones (CDPZs), which restrict land use activities to protect water quality. In South Canterbury, 75 Community Drinking Water Protection Zones were introduced in 2017 and are part of the Land and Water Regional Plan – we are one of just a few councils in New Zealand to have these additional measures.

The size of the zone reflects the nature of the water source, for example, shallow bores may have a larger protection zone than deep, well-protected sources.

These zones are designed to reduce the risk of faecal bacteria, chemicals and other contaminants entering community drinking water supplies, rather than give specific protection against nitrate contamination.

We have other rules, like nitrogen fertiliser restrictions, to reduce nitrate loss to water across Canterbury but these aren’t always able to counter the impacts of extreme weather.

More information