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Elevated E.coli levels have once again been detected in a bore feeding from the Lower Waitaki Aquifer, the Otago Regional Council confirmed yesterday.
Faecal source tracking from water quality testing on October 18 showed the presence of a cow marker, which meant it was likely the source of the E.coli was cattle.
Results showed an elevated E.coli level measured at 41MPN/100ml. The recommended level for safe drinking water is less than 1MPN/100ml.
ORC director of science, hazards and engineering, Dr Gavin Palmer, said additional testing was being carried out on nearby bores to see if the source of the contamination could be identified.
"We increased our water sampling from quarterly to monthly after the first results showed up in September and have built faecal source tracking into the monitoring programme."
The same bore tested positive in September, when an E.coli level of 63MPN/100ml was recorded.
The ORC recommended Lower Waitaki Plains residents who sourced their drinking water from private bores should assume it was contaminated unless they had effective disinfection in place.