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For Mosgiel residents to return to drinking bore water would require new infrastructure costing up to $20 million, the Dunedin City Council says.
In December, the council decided to switch Mosgiel residents to the town water supply from the Mount Grand treatment plant.
The move prompted the Mosgiel-Taieri Community Board to ask the council to investigate the feasibility of switching Mosgiel residents back to treated bore water.
Council 3 Waters group manager Tom Dyer accepted the request and told the board the investigation findings would be available at a board meeting at Coronation Hall last week.
Mr Dyer, speaking at that meeting, said that the investigation was continuing and the findings would be available at the board meeting to be held next month.
At the meeting last week, Mr Dyer told the board members and 12 people in the public gallery about the investigation so far.
The cost of piping the seven bores in Mosgiel to a central treatment plant for distribution would need new infrastructure costing between $15 million and $20 million, Mr Dyer said.
At the treatment plant, the bore water would need to be chlorinated, he said.
Faecal matter had been detected at the seven bore sites before and similar incidents were forecast to increase, he said.
Some of the water entering the aquifer and the drinking water supply were from unknown sources, he said.
''Prior to December, we had no way of preventing that water, and any contamination in the water, from causing harm to people's health ... the obvious and immediately achievable solution was to send water from town and shut down the bores,'' he said.