April 17, 2026
Tinwald’s drinking water source could exceed safe nitrate limits within a decade, forcing the council to weigh up an $11 million fix or piping it across the river.
A report to the Ashburton District Council’s three waters committee warned the suburb’s current bore may soon breach drinking water standards, prompting urgent debate over whether to drill deeper, treat the water, or shift the supply exclusively from across the Ashburton River.
The water sourced from the Tinwald bore has elevated nitrate levels that are currently below the maximum acceptable value (MAV) for drinking water (11.3 mg/L).
A 2024 report from Aqualinc determined the Tinwald bore would likely have nitrate levels exceeding the MAV by 2029-2033 based on the trends and suggested that lower nitrate water is likely present in the deeper aquifers.
A feasibility report tabled to the three waters committee on Wednesday concluded that seeking deeper groundwater source is ”a feasible, though uncertain, option for securing a lower nitrate” source.
It also stated a deeper source should be considered a temporary measure until a new water main on the second Ashburton River Bridge, to complement the water main across the existing bridge, offers a longer-term solution.
The report to the committee stated that due to the high cost of removing nitrates from the water, the preferred option is to drill a new bore within the existing water treatment plant site.
Asset manager Andy Guthrie estimated the cost for drilling a new or deeper bore at $500,000
He said there is money budgeted for an additional bore, and the decision will be on where to put it.
However drilling a new or deeper bore in the existing site does not guarantee a long-term supply of potable water and nitrate treatment equipment - estimated at around $11m in cost - could still then be needed.
Cr Phill Everest was alarmed that the council would even consider continuing to take water from within a known nitrate plume area “if we can just take it across the bridge”.
“Why are we spending money in an area we don’t need to?
“I’m distinctly uncomfortable with spending a lot of money on a site which we already know is high nitrate when we have other sources available.”
Everest sought clarity if there was sufficient water supply on the Ashburton town side to deliver to Tinwald.
Glasner said there is, but how much the council can take is capped by the resource consent and a key question would be its long-term viability with the continued growth in Tinwald.
Everest felt it was a simple solution.
Rather than spending $11m on a nitrate stripping machine, and already $1.8m to get extra water across the new bridge, then “surely the way better option is actually to dig another well on [the town side] of the river, which we already know is low nitrate”.
Glasner said a report will be prepared to gauge “if it is suitable to supply Tinwald purely from the Ashburton side of the bridge”.
Infrastructure manager Neil McCann said the current Tinwald bore site had been chosen because it “had a good yield of water”.
“Where we have drilled elsewhere away from the plume, the yield hasn’t been good.
“Unfortunately, the quality is getting to a position now we have to really start thinking of other sites, locations and other sources.”
A report will now come back to the committee to consider potential solutions other than drilling a new bore to make a recommendation to the council.
By Jonathan Leask
Tinwald’s drinking water source could exceed safe nitrate limits within a decade, forcing the council to weigh up an $11 million fix or piping it across the river.
A report to the Ashburton District Council’s three waters committee warned the suburb’s current bore may soon breach drinking water standards, prompting urgent debate over whether to drill deeper, treat the water, or shift the supply exclusively from across the Ashburton River.
The water sourced from the Tinwald bore has elevated nitrate levels that are currently below the maximum acceptable value (MAV) for drinking water (11.3 mg/L).
A 2024 report from Aqualinc determined the Tinwald bore would likely have nitrate levels exceeding the MAV by 2029-2033 based on the trends and suggested that lower nitrate water is likely present in the deeper aquifers.
A feasibility report tabled to the three waters committee on Wednesday concluded that seeking deeper groundwater source is ”a feasible, though uncertain, option for securing a lower nitrate” source.
It also stated a deeper source should be considered a temporary measure until a new water main on the second Ashburton River Bridge, to complement the water main across the existing bridge, offers a longer-term solution.
The report to the committee stated that due to the high cost of removing nitrates from the water, the preferred option is to drill a new bore within the existing water treatment plant site.
Asset manager Andy Guthrie estimated the cost for drilling a new or deeper bore at $500,000
He said there is money budgeted for an additional bore, and the decision will be on where to put it.
However drilling a new or deeper bore in the existing site does not guarantee a long-term supply of potable water and nitrate treatment equipment - estimated at around $11m in cost - could still then be needed.
Cr Phill Everest was alarmed that the council would even consider continuing to take water from within a known nitrate plume area “if we can just take it across the bridge”.
“Why are we spending money in an area we don’t need to?
“I’m distinctly uncomfortable with spending a lot of money on a site which we already know is high nitrate when we have other sources available.”
Everest sought clarity if there was sufficient water supply on the Ashburton town side to deliver to Tinwald.
Glasner said there is, but how much the council can take is capped by the resource consent and a key question would be its long-term viability with the continued growth in Tinwald.
Everest felt it was a simple solution.
Rather than spending $11m on a nitrate stripping machine, and already $1.8m to get extra water across the new bridge, then “surely the way better option is actually to dig another well on [the town side] of the river, which we already know is low nitrate”.
Glasner said a report will be prepared to gauge “if it is suitable to supply Tinwald purely from the Ashburton side of the bridge”.
Infrastructure manager Neil McCann said the current Tinwald bore site had been chosen because it “had a good yield of water”.
“Where we have drilled elsewhere away from the plume, the yield hasn’t been good.
“Unfortunately, the quality is getting to a position now we have to really start thinking of other sites, locations and other sources.”
A report will now come back to the committee to consider potential solutions other than drilling a new bore to make a recommendation to the council.
By Jonathan Leask
