A big job ahead for the Otago Regional Council to remedy an E.coli contamination spread throughout 119 bores

Groundwater on the Lower Waitaki plains, north of Oamaru, has become contaminated and the water, which supplies houses, is not drinkable.

The Regional Council's chief executive, Sarah Gardner, says no one has contacted the council to say they're without water, as they may have suitable treatment or tanks for rain water.

She says an investigation's started, but has no idea when the water might be potable again.

Gardner says it'll take some time to even find the source - and only then can they start to work out how to make the water safe again.