Continuing low temperatures are thought to be behind a burst chlorination dosing line at the western reservoir at Wanaka this morning, Queenstown Lakes District Council utilities general manager Mark Kunath said.

"At 4.26am this morning Lakes Contract Services detected a low chlorination alarm in the system. It appears that the feeder pipe had frozen and then split in the extreme low temperatures," Mr Kunath said.

Having detected the problem, the contractor commenced hand dosing the supply at 9.30am.

"It is possible that the supply was not chlorinated to acceptable levels for a period of no more than two hours from 7.30-9.30am," Mr Kunath said.

As a precaution water testing was carried out but results would not be available until tomorrow at the earliest, he said. The supply services households from Stoney Creek to Penrith Park.

Mr Kunath was confident that the contractor had worked hard to identify and correct the problem.

"Although the infrastructure is designed to withstand the anticipated low temperatures of the winter season, the consistently low temperatures have, in this instance taken their toll. The line has now been repaired and re-laid at a greater depth to avoid further problems," Mr Kunath said.

The council would release the findings of the tests tomorrow.

Meanwhile it's important that we let the community know that water used over a brief period this morning may not have been fully treated.