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Last month it was announced the testing of bore samples concluded the bacterial count made the water unfit for human consumption without treatment.
During routine testing, an E. coli spike of 150cfu/100ml was recorded in the bores. The drinking water standard is 1cfu/100ml.
In a statement, council chief executive Sarah Gardner said the inconclusive result was due to a low concentration of E. coli in the sample at the time of testing.
Regional council scientists would test for contamination sources ''concurrently'' with any further spikes while the E. coli concentration was high enough to allow them to determine it.
''Determining the source requires a different type of test to the routine water sampling we undertake. Having high concentrations of E, coli present during a spike may allow our scientists to determine what's causing the issue at that exact point in time.''
Waitaki Bridge village resident Peter Whitlock, who has criticised the regional council for its approach in dealing with the issue, said the latest test result did not come as a shock.
He had been drinking the aquifer water for 30 years, with no ill effects.
''It comes as no surprise at all that they can't determine where it has come from. There is nothing for us to worry about down here. If they were worried, they would have tested our water. It doesn't seem fair that after years of having clear and clean water we are suddenly polluted.''
He recently sent a sample of water from his home to a Dunedin laboratory to be tested, but was yet to receive the results.
Mrs Gardner advised people in the affected area to ''remain vigilant'' and recommended residents not drink the water.
-By Daniel Birchfield