Microbes may be cause of town's contaminated water supply

The source of the contamination of Alexandra's water supply may have been found, but the Central Otago District Council said it could be some time before it went away.

Chemicals released by microbes into the groundwater have been identified as a possible source of the unpleasant smell and taste of the water from the town's boreholes.

However, it could be another week before tests confirm that possibility.

Meanwhile, rumours are rife around town that the water problem is caused by battery acid leaching from the old tip site.

Central Otago District Council utilities engineer Rob Lei said the rumours were unfounded, and if it was battery acid the water wouldn't have the earthy, musty taste people had been complaining about.

He said the problem appeared to have migrated to all but one of the boreholes, which made it difficult to manage.

The problem arose just before the Alexandra Blossom Festival and got progressively worse during that weekend and had continued for the past 10 days.

"It was hoped that the situation would improve with the isolation of the affected boreholes, but this has not been the case," he said.

Although not a health risk, the contamination was not able to be removed because the source was within the groundwater.

The council hoped the contamination would naturally decline over time," Me Lei said. "Council is consulting with relevant specialists to try and determine the cause of the problem, however this has been inconclusive to date.

"The most likely scenario at present is believed to be chemicals released into the water by microbes in the ground." It was a seasonal problem with many water supplies around the world, he said.

"These chemicals only require trace amounts to trigger such taste and odour problems and are harmless in the quantities found." Further laboratory analysis was being carried out to confirm that possibility, but would take at least a week to process.

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