A diesel spill at Christchurch Men’s Prison has triggered a warning for nearby residents on private water supplies, with authorities advising some to immediately stop using their bore water for drinking, cooking and toothbrushing.

Corrections confirmed on Thursday that diesel entered the ground on 25 May after an issue with one of the prison’s fuel tanks. A positive test result was returned on 6 June from a bore located about 200 metres outside the prison perimeter, prompting a precautionary response.

“This does not impact residents in the area on town water supply and it does not impact anyone in the wider Christchurch area,” said Commissioner Custodial Services Leigh Marsh.

“Corrections has advised a small number of neighbouring properties at Christchurch Men’s Prison to temporarily stop using private bore water for drinking and cooking,” Marsh said. “We have visited approximately 40 properties by door knocking and leaving a letter with further information – and have advised a small number of occupied properties that they should stop using water from their private bores.”

Corrections said bottled water was provided to residents who requested it, and anyone who was not contacted directly or did not receive a letter could continue using their bore water as normal.

In a letter delivered to affected residents, Environment Canterbury said, “It is possible diesel may enter groundwater and downgradient wells could be impacted in the coming days. Overall, the risk to surrounding water supplies is unknown.”

Dr Elaine Moriarty, Water and Land Science Manager at Environment Canterbury, said the National Public Health Service recommends residents “immediately discontinue using your private supply for domestic use and food preparation.”

“This includes drinking water, cooking or preparing food, and toothbrushing,” she said. Showering, bathing, and washing clothes remain safe.

The letter said residents should also avoid using bore water for irrigation or stock use and seek medical advice if feeling unwell.

Corrections said the nearest residential-use bore is approximately 1.4 kilometres from the leak site. “While Corrections has received a positive result, we are continuing to undertake further testing and analysis. We will continue to keep impacted residents updated,” Marsh said.

Key agencies including Environment Canterbury, Taumata Arowai and Fire and Emergency NZ have been notified, and further water testing is ongoing.

Residents with concerns or questions have been encouraged to contact Corrections directly at [email protected]