A low dose of chlorine is being added to Arrowtown’s water supply until the three tanks which make up the town’s reservoir are cleaned as part of routine maintenance.

QLDC Chief Engineer Ulrich Glasner said that one of the three tanks was empty following a leak late last year. Inspection found that roots from nearby trees had intruded into the tank, causing cracking. Once the repairs were complete, the tank would be thoroughly cleaned before being brought back into use. After that, each of the remaining two tanks would be also emptied, checked and cleaned.

Until then, a low dose of chlorine would be maintained in the supply as an added precaution to supplement the new ultra-violet treatment supply, Mr Glasner said.

“Once the tanks have all been checked, cleaned and recommissioned, we expect that chlorination will be discontinued. This is a precaution to ensure that we continue to meet the drinking water standards, because from time to time over the last few weeks our regular testing has found isolated incidences of E. coli.”

Mr Glasner said the low dose of chlorine meant there was no need for households to boil water.

The Queenstown and Wanaka water supplies are permanently chlorinated.